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Unexpected indent in python [duplicate]

I have a Python script:
if True:
if False:
print('foo')
print('bar')
However, when I attempt to run my script, Python raises an IndentationError:
File "script.py", line 4
print('bar')
^
IndentationError: unindent does not match any outer indentation level
I kept playing around with my program, and I was able to produce four errors in total:
IndentationError: unexpected indent
IndentationError: expected an indented block
TabError: inconsistent use of tabs and spaces in indentation
IndentationError: unindent does not match any outer indentation level
What do these errors mean? What am I doing wrong? How can I fix my code?
Note: This is an attempt at a canonical question because I see many similar posts every month. This is not a duplicate of existing questions about unindents or unexpected indents because they only deal with one type of indentation error each, and I'm looking to cover them all in one place.
It's also possible to have logically incorrect indentation that does not cause an error message. One common form of this is attaching else: to a for or while loop rather than (as intended) the corresponding if:. See Else clause on Python while statement if you need to close questions where OP did that.

Why does indentation matter?
In Python, indentation is used to delimit blocks of code. This is different from many other languages that use curly braces {} to delimit blocks such as Java, Javascript, and C. Because of this, Python users must pay close attention to when and how they indent their code because whitespace matters.
When Python encounters a problem with the indentation of your program, it either raises an exception called IndentationError or TabError.
A little history
The historical reasons for why Python uses indentation vs the arguably more commonly accepted curly braces {} is outlined in an article of the history of Python by Guido van Rossum - the creator of Python:
Python’s use of indentation comes directly from ABC, but this idea didn’t originate with ABC--it had already been promoted by Donald Knuth and was a well-known concept of programming style. (The occam programming language also used it.) However, ABC’s authors did invent the use of the colon that separates the lead-in clause from the indented block. After early user testing without the colon, it was discovered that the meaning of the indentation was unclear to beginners being taught the first steps of programming. The addition of the colon clarified it significantly: the colon somehow draws attention to what follows and ties the phrases before and after it together in just the right way.
How do I indent my code?
The basic rule for indenting Python code (considering that you treat the entire program as a "basic block") is: The first statement in a basic block, and each subsequent statement after it must be indented by the same amount.
So technically the following Python program is correct:
def perm(l):
# Compute the list of all permutations of l
if len(l) <= 1:
return [l]
r = []
for i in range(len(l)):
s = l[:i] + l[i+1:]
p = perm(s)
for x in p:
r.append(l[i:i+1] + x)
return r
However, as you can probably tell from above, randomly indenting your code makes is extremely hard to read and follow the flow of the program. It's better to be consistent and follow a style.
PEP 8 -- the Python style guide -- says:
Use 4 spaces per indentation level.
That is, each statement that is starting a new block and each subsequent statement in the new block, should be indented four spaces from the current indentation level. Here is the above program indented according to the PEP8 style guide:
def perm(l):
# Compute the list of all permutations of l
if len(l) <= 1:
return [l]
r = []
for i in range(len(l)):
s = l[:i] + l[i+1:]
p = perm(s)
for x in p:
r.append(l[i:i+1] + x)
return r
Can I still use tabs?
Python realizes that some people still prefer tabs over spaces and that legacy code may use tabs rather than spaces, so it allows the use of tabs as indentation. PEP8 touches on this topic:
Spaces are the preferred indentation method.
Tabs should be used solely to remain consistent with code that is already indented with tabs.
Note however the one big caveat is not to use both tabs and spaces for indentation. Doing so can cause all kinds of strange hard to debug indentation errors. Python expands tabs to the next 8th column, but if your editor is set to a tab size of 4 columns, or you you use spaces as well as tabs, you can easily produce indented code that looks fine in your editor, but Python will refuse to run. The Python 3 compiler explicitly rejects any program containing an ambiguous mixture of tabs and spaces, usually by raising a TabError. However, by default, mixing tabs and spaces is still allowed in Python 2, but it is highly recommended not to use this "feature". Use the -t and -tt command line flags to force Python 2 to raise a warning or (preferably) an error respectively. PEP8 also discusses this topic:
Python 3 disallows mixing the use of tabs and spaces for indentation.
Python 2 code indented with a mixture of tabs and spaces should be converted to using spaces exclusively.
When invoking the Python 2 command line interpreter with the -t option, it issues warnings about code that illegally mixes tabs and spaces. When using -tt these warnings become errors. These options are highly recommended!
What does "IndentationError: unexpected indent" mean?
Problem
This error occurs when a statement is unnecessarily indented or its indentation does not match the indentation of former statements in the same block. For example, the first statement in the program below is unnecessarily indented:
>>> print('Hello') # this is indented
File "<stdin>", line 1
print('Hello') # this is indented
^
IndentationError: unexpected indent
In this example, the can_drive = True line in the if block does not match the indentation of any former statement:
>>> age = 10
>>> can_drive = None
>>>
>>> if age >= 18:
... print('You can drive')
... can_drive = True # incorrectly indented
File "<stdin>", line 3
can_drive = True # incorrectly indented
^
IndentationError: unexpected indent
Fix
The fix for this error is to first make sure the problematic line even needs to be indented. For example, the above example using print can be fixed simply be unindenting the line:
>>> print('Hello') # simply unindent the line
Hello
However, if you are sure the line does need to be indented, the indentation needs to match that of a former statement in the same block. In the second example above using if, we can fix the error by making sure the line with can_drive = True is indented at the same level as the former statements in the if body:
>>> age = 10
>>> can_drive = None
>>>
>>> if age >= 18:
... print('You can drive')
... can_drive = True # indent this line at the same level.
...
What does "IndentationError: expected an indented block" mean?
(This might also occur as SyntaxError: unexpected EOF while parsing in Python 3.8 or lower.)
Problem
This error occurs when Python sees the 'header' for a compound statement, such as if <condition>: or while <condition>: but the compound statement's body or block is never defined. For example in the code below we began an if statement, but we never define a body for the statement:
>>> if True:
...
File "<stdin>", line 2
^
IndentationError: expected an indented block
In this second example, we began writing a for loop, but we forget to indent the for loop body. So Python still expects an indented block for the for loop body:
>>> names = ['sarah', 'lucy', 'michael']
>>> for name in names:
... print(name)
File "<stdin>", line 2
print(name)
^
IndentationError: expected an indented block
Comments don't count as bodies:
>>> if True:
... # TODO
...
File "<stdin>", line 3
^
IndentationError: expected an indented block
Fix
The fix for this error is to simply include a body for the compound statement.
As shown above, a common mistake by new users is that they forget to indent the body. If this is the case, make sure each statement meant to be included in the compound statement's body is indented at the same level under the compound statement's beginning. Here is the above example fixed:
>>> names = ['sarah', 'lucy', 'michael']
>>> for name in names:
... print(name) # The for loop body is now correctly indented.
...
sarah
lucy
michael
Another common case is that, for some reason, a user may not want to define an actual body for the compound statement, or the body may be commented out. In this case, the pass statement can be used. The pass statement can be used anywhere Python expects one or more statements as a placeholder. From the documentation for pass:
pass is a null operation — when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed, for example:
def f(arg): pass # a function that does nothing (yet)
class C: pass # a class with no methods (yet)
Here is the above example with the if statement fixed by using the pass keyword:
>>> if True:
... pass # We don't want to define a body.
...
>>>
What does "IndentationError: unindent does not match any outer indentation level" mean?
Problem
This error occurs when you unindent a statement, but now the indentation level of that statement does not match that of any former statement. For example, in the below code we unindent the second call to print. However, the indentation level does not match that of any former statement:
>>> if True:
... if True:
... print('yes')
... print()
File "<stdin>", line 4
print()
^
IndentationError: unindent does not match any outer indentation level
This error is especially hard to catch because even one space will cause your code to fail.
Fix
The fix is to ensure that when you unindent a statement, the indentation level matches that of a former statement. Consider the above example once again. In the example, I want the second call to print to be in the first if statements body. So I need to make sure that that line's indentation level matches that of the former statements in the first if statement's body:
>>> if True:
... if True:
... print('yes')
... print() # indentation level now matches former statement's level.
...
yes
>>>
I'm still getting an IndentationError but my program appears to be correctly indented. What do I do?
If your program visually appears to have correct indentation, but your still getting an IndentationError you have most likely mixed tabs with spaces. This will sometimes cause Python to raises strange errors. See the subsection Special cases under What does "TabError: inconsistent use of tabs and spaces in indentation" mean? for an more in-depth explanation of the problem.
What does "TabError: inconsistent use of tabs and spaces in indentation" mean?
Problem
This error only occurs when you attempt to mix tabs and spaces as indentation characters. As said above, Python will not allow your program to contain a mix of tabs and spaces, and will raise the specific exception TabError if it finds you have. For example, in the program below, a mix of tabs and spaces is used for indentation:
>>> if True:
... if True:
... print()
... print()
... print()
File "<stdin>", line 5
print()
^
TabError: inconsistent use of tabs and spaces in indentation
Here is a picture which visually shows the whitespace in the above program. Gray dots are spaces, and gray arrows are tabs:
We can see we have indeed mixed spaces and tabs for indentation.
Special cases
Note Python will not always raise a TabError if you mix tabs and spaces into your program. If the program indentation is unambiguous, Python will allow tabs and spaces to be mixed. For example:
>>> if True:
... if True: # tab
... pass # tab, then 4 spaces
...
>>>
And sometimes Python simply chokes on the mixture of tabs and spaces and erroneously raises an IndentationError exception when a TabError would be more appropriate. Another example:
>>> if True:
... pass # tab
... pass # 4 spaces
File "<stdin>", line 3
pass # 4 spaces
^
IndentationError: unindent does not match any outer indentation level
As you can see, running your code this way can create mysterious errors. Even though the program visually appears to be fine, Python became confused trying to parse the tabs and spaces used for indention and errored out.
These are excellent examples that demonstrate why to never mix tabs and spaces and make use of the -t and -tt interpreter flags when using Python 2.
Fix
If your program is short, probably the easiest and quickest fix is to simply re-indent the program. Make sure each statement is indented by four spaces per indention level (see How do I indent my code?).
However, if you already have a large program that you've mixed tabs and spaces into, there are automated tools that can be used to convert all of your indentation to just spaces.
Many editors such as PyCharm and SublimeText have options to automatically convert tabs to spaces. There are also several on-line tools such as Tabs To Spaces or Browserling that allow you to quickly re-indent your code. There are also tools written in Python. autopep8 for example can automatically re-indent your code and fix other indentation errors as well.
Even the best tools though will sometimes not be able to fix all of your indentation errors and you'll have to fix them manually. That's why it's important to always properly indent your code from the start.
A note about "SyntaxError" related indentation problems
Although not often, sometimes certain SyntaxError exceptions are raised due to incorrect indentation. For example, look at the code below:
if True:
pass
pass # oops! this statement should be indented!.
else:
pass
When the above code is run, a SyntaxError is raised:
Traceback (most recent call last):
File "python", line 4
else:
^
SyntaxError: invalid syntax
Although Python raises a SyntaxError, the real problem with the above code is that the second pass statement should be indented. Because the second pass isn't indented, Python doesn't realize that the previous if statement and the else statement are meant to be connected.
The fix for this type of error is to simply correctly re-indent your code. To see how to properly indent your code, see the section How do I indent my code?.
I'm still having a hard time with Python's indentation syntax. What do I do?
Don't get discouraged if you're still struggling. It can take time to get use to
Python's whitespace syntax rules. Here are some tips to help:
Get an editor that will tell you when you have an indentation error. Some goods ones are as said above are, PyCharm, SublimeText, and Jupyter Notebook.
When you indent your code, count out loud to yourself how many times you press the space-bar (or tab key). For example, if you needed to indent a line by four spaces, you would say out loud "one, two, three, four" while simultaneously pressing the space-bar each time. It sounds silly, but it helps train your brain to think about how deep you're indenting your code.
If you have an editor, see if it has an option to automatically convert tabs to spaces.
View others' code. Browse github or Stackoverflow and see examples of Python code.
Just write code. That's the single best way to get better. The more you write Python code, the better you'll get.
Resources used
https://en.wikipedia.org/
https://docs.python.org/3/
http://python-history.blogspot.com/2009/02/early-language-design-and-development.html
https://www.python.org/dev/peps/pep-0008/

Sublime Text 3
If it happens that you code in Sublime Text 3, this could help you with indentations problemes
In Sublime Text, while editing a Python file:
Sublime Text menu > Preferences > Settings - Syntax Specific :
Python.sublime-settings
{
"tab_size": 4,
"translate_tabs_to_spaces": true
}

You see, you have a tiny error.
if True:
if False:
print('foo')
print('bar')
You were supposed to do:
if True:
if False:
print('foo')
print('bar')
As you can see your print is only indented 3 spaces, it is supposed to be indented 4 spaces.

Historical note for Python 2
By default, Python 2 allowed tabs and spaces to be mixed, and would not produce an error by default. Passing the -tt option to Python 2.x causes it to raise an exception in the same cases that 3.x does, and -t causes a warning instead. The full details are explained at Python's interpretation of tabs and spaces to indent.
Note in particular that tabs are treated as 8 spaces (rather, they effectively increase the number of perceived spaces up to the next multiple of 8). Thus, if you were displaying the code with a standard 4-space indent, but have mixed spaces and tabs, you could end up with code that satisfies the indentation rules, but is not considered to be indented the same way that it looks.
As a result, you could get all kinds of other errors. For example:
# in 2.x
def example():
def nested(): # suppose this is indented with a tab
x = [1] # and this with two tabs
print x[0] + 1 # but this with 8 spaces instead of a tab
nested()
(Note that Stack Overflow's Markdown rendering will show the indentation as spaces even if I use tabs.)
That gives a NameError, since print x is no longer inside the nested function and x is out of scope in the outer example. Similarly, we could easily create a TypeError by giving example a local x = 1, or ValueError by giving it a local x = [].

Quick checklist
Incorrect indentation most commonly results in IndentationError, but it can also result in TabError (a sub-type of IndentationError) or SyntaxError (the indentation itself was legal, but it caused other code to have a syntax error). Indentation that is valid for Python code, but wrong for the programmer's intent, causes logical errors (the code doesn't raise an exception, but does something wrong).
It is strongly recommended not to use tabs for indentation. In 2.x, running Python with the -tt command line argument causes it to raise the same TabError, which is useful for finding problems.
The community standard, laid out in PEP 8, is to use four spaces per level of indentation.
Statements like if, for, def and class that end with a colon :, need an indented block after them:
if x:
do_y() # <- this must be indented
Blocks cannot be empty. Use the pass statement if nothing should happen:
if x:
pass # this statement does nothing, except make the block non-empty
Code within a block must have the same indentation:
if x:
do_y()
do_z() # this needs to line up with do_y()
The first line of code that lines up with the opening statement, or a lower level of indentation, is outside the block:
if x:
do_y()
do_z() # this happens regardless of the x value
# cannot write `else`: here; that is a syntax error
for i in range(10):
if x:
do_y()
do_z() # both the `if` and `for` blocks are ended
Python interprets tabs as expanding to the next 8th column; but in 3.x, indentation that mixes spaces and tabs must have the exact same pattern to count as the same indentation (and to indent further requires having the same pattern as a prefix). Failure to get this right results in TabError.
while and for loops in Python may have an else clause, which executes if the loop complete normally rather than via break. This is a common source of logical errors:
for i in range(10):
if i % 2:
print(f'{i} is odd')
else: # wrongly indented
print(f'{i} is even') # only happens once, and claims 9 is even!

Quick fix for Sublime users:
Press Ctrl-H to access Find and Replace
In Find: Type 4 spaces
In Replace: Copy and paste a tab from somewhere in your code
Click Replace All

I'm getting this error "IndentationError: unexpected indent" [duplicate]

How do I rectify the error "unexpected indent" in Python?

Python uses spacing at the start of the line to determine when code blocks start and end. Errors you can get are:
Unexpected indent. This line of code has more spaces at the start than the one before, but the one before is not the start of a subblock (e.g., the if, while, and for statements). All lines of code in a block must start with exactly the same string of whitespace. For instance:
>>> def a():
... print "foo"
... print "bar"
IndentationError: unexpected indent
This one is especially common when running Python interactively: make sure you don't put any extra spaces before your commands. (Very annoying when copy-and-pasting example code!)
>>> print "hello"
IndentationError: unexpected indent
Unindent does not match any outer indentation level. This line of code has fewer spaces at the start than the one before, but equally it does not match any other block it could be part of. Python cannot decide where it goes. For instance, in the following, is the final print supposed to be part of the if clause, or not?
>>> if user == "Joey":
... print "Super secret powers enabled!"
... print "Revealing super secrets"
IndendationError: unindent does not match any outer indentation level
Expected an indented block. This line of code has the same number of spaces at the start as the one before, but the last line was expected to start a block (e.g., if, while, for statements, or a function definition).
>>> def foo():
... print "Bar"
IndentationError: expected an indented block
If you want a function that doesn't do anything, use the "no-op" command pass:
>>> def foo():
... pass
Mixing tabs and spaces is allowed (at least on my version of Python), but Python assumes tabs are 8 characters long, which may not match your editor. Don't mix tabs and spaces. Most editors allow automatic replacement of one with the other. If you're in a team, or working on an open-source project, see which they prefer.
The best way to avoid these issues is to always use a consistent number of spaces when you indent a subblock, and ideally use a good IDE that solves the problem for you. This will also make your code more readable.

In Python, the spacing is very important. This gives the structure of your code blocks.
This error happens when you mess up your code structure, for example like this:
def test_function():
if 5 > 3:
print "hello"
You may also have a mix of tabs and spaces in your file.
I suggest you use a Python syntax aware editor, like PyScripter, or NetBeans.

Run your code with the -tt option to find out if you are using tabs and spaces inconsistently.

Turn on visible whitespace in whatever editor you are using and turn on replace tabs with spaces.
While you can use tabs with Python, mixing tabs and space usually leads to the error you are experiencing. Replacing tabs with four spaces is the recommended approach for writing Python code.

By using correct indentation. Python is white space aware, so you need to follow its indentation guidelines for blocks or you'll get indentation errors.

Run the following command to get it solved:
autopep8 -i <filename>.py
This will update your code and solve all indentation errors :)

If you're writing Python using Sublime Text and are getting indentation errors,
Menu View → Indentation → Convert indentation to spaces
The issue I'm describing is caused by the Sublime Text editor. The same issue could be caused by other editors as well. Essentially, the issue has to do with Python wanting to treat indentations in terms of spaces versus various editors coding the indentations in terms of tabs.

One issue which doesn't seem to have been mentioned is that this error can crop up due to a problem with the code that has nothing to do with indentation.
For example, take the following script:
def add_one(x):
try:
return x + 1
add_one(5)
This returns an IndentationError: unexpected unindent when the problem is of course a missing except: statement.
My point: check the code above where the unexpected (un)indent is reported!

Make sure you use the option "Insert spaces instead of tabs" in your editor. Then you can choose you want a tab width of, for example 4. You can find those options in gedit under menu Edit → preferences → Editor.
Bottom line: use spaces, not tabs

This error can also occur when pasting something into the Python interpreter (terminal/console).
Note that the interpreter interprets an empty line as the end of an expression, so if you paste in something like
def my_function():
x = 3
y = 7
the interpreter will interpret the empty line before y = 7 as the end of the expression, i.e. that you're done defining your function, and the next line - y = 7 will have incorrect indentation because it is a new expression.

If the indentation looks ok then have a look to see if your editor has a "View Whitespace" option. Enabling this should allow to find where spaces and tabs are mixed.

It depends in the context. Another scenario which wasn't yet covered is the following. Let's say you have one file with a class with a specific method in it
class Scraper:
def __init__(self):
pass
def scrape_html(self, html: str):
pass
and in the bottom of the file you have something like
if __name__ == "__main__":
# some
# commands
# doing
# stuff
making it the whole file look like this
class Scraper:
def __init__(self):
pass
def scrape_html(self, html: str):
pass
if __name__ == "__main__":
# some
# commands
# doing
# stuff
If in scrape_html() you open up, for example, an if/else statement
class Scraper:
def __init__(self):
pass
def scrape_html(self, html: str):
if condition:
pass
else:
if __name__ == "__main__":
parser = argparse.ArgumentParser()
You'll need to add pass or whatever you want to to that else statement or else you'll get
Expected indented block
Unindent not expected
Expected expression
and in the first row
Unexpected indentation
Adding that pass would fix all of these four problems.

There is a trick that always worked for me:
If you got an unexpected indent and you see that all the code is perfectly indented, try opening it with another editor and you will see what line of code is not indented.
It happened to me when I used Vim, gedit, or editors like that.
Try to use only one editor for your code.

Simply copy your script, and put it under """ your entire code """ ...
Specify this line in a variable... like,
a = """ your Python script """
print a.replace("Here please press the tab button. It will insert some space", " here simply press the space bar four times.")
#
# Here we are replacing tab space by four character
# space as per the PEP 8 style guide...
#
# Now execute this code. In the Sublime Text
# editor use Ctrl + B. Now it will print
# indented code in the console. That's it.

All you need to do is remove spaces or tab spaces from the start of the following code:
from django.contrib import admin
# Register your models here.
from .models import Myapp
admin.site.register(Myapp)

Notepad++ was giving the tab space correct, but the indentation problem was finally found in the Sublime Text editor.
Use the Sublime Text editor and go line by line.

Indentation in Python is important and this is just not for code readability, unlike many other programming languages.
If there is any white space or tab in your code between consecutive commands, Python will give this error as Python is sensitive to this. We are likely to get this error when we do copy and paste of code to any Python.
Make sure to identify and remove these spaces using a text editor like Notepad++ or manually remove the whitespace from the line of code where you are getting an error.
# Step 1: Gives an error
L = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
print(L[2: ])
# Step 2: L = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]print(L[2: ])
# Step 3: No error after space was removed
L = [[1, 2, 3], [4, 5, 6], [7, 8, 9, 10]]
print(L[2: ])
# Output: [[7, 8, 9, 10]]

It depends on the context, but an indentation error is often caused by using tabs instead of spaces.
Here are some steps you can take to correct this:
Copy the tabs or spaces that are causing the error
Do a find and replace in your IDE (usually Ctrl + H).
Paste the copied tabs or spaces into the "Find" search bar, and then replace them all with four spaces (assuming that your IDE uses four spaces as a "good" indentation)
This error also happens a lot if you are copying and pasting code from external sources into your IDE, because the formatting elsewhere may not match your IDE's definition for what counts as a "good" indentation.

Asking user for input for a lists [duplicate]

I have a Python script:
if True:
if False:
print('foo')
print('bar')
However, when I attempt to run my script, Python raises an IndentationError:
File "script.py", line 4
print('bar')
^
IndentationError: unindent does not match any outer indentation level
I kept playing around with my program, and I was able to produce four errors in total:
IndentationError: unexpected indent
IndentationError: expected an indented block
TabError: inconsistent use of tabs and spaces in indentation
IndentationError: unindent does not match any outer indentation level
What do these errors mean? What am I doing wrong? How can I fix my code?
Note: This is an attempt at a canonical question because I see many similar posts every month. This is not a duplicate of existing questions about unindents or unexpected indents because they only deal with one type of indentation error each, and I'm looking to cover them all in one place.
It's also possible to have logically incorrect indentation that does not cause an error message. One common form of this is attaching else: to a for or while loop rather than (as intended) the corresponding if:. See Else clause on Python while statement if you need to close questions where OP did that.

Why does indentation matter?
In Python, indentation is used to delimit blocks of code. This is different from many other languages that use curly braces {} to delimit blocks such as Java, Javascript, and C. Because of this, Python users must pay close attention to when and how they indent their code because whitespace matters.
When Python encounters a problem with the indentation of your program, it either raises an exception called IndentationError or TabError.
A little history
The historical reasons for why Python uses indentation vs the arguably more commonly accepted curly braces {} is outlined in an article of the history of Python by Guido van Rossum - the creator of Python:
Python’s use of indentation comes directly from ABC, but this idea didn’t originate with ABC--it had already been promoted by Donald Knuth and was a well-known concept of programming style. (The occam programming language also used it.) However, ABC’s authors did invent the use of the colon that separates the lead-in clause from the indented block. After early user testing without the colon, it was discovered that the meaning of the indentation was unclear to beginners being taught the first steps of programming. The addition of the colon clarified it significantly: the colon somehow draws attention to what follows and ties the phrases before and after it together in just the right way.
How do I indent my code?
The basic rule for indenting Python code (considering that you treat the entire program as a "basic block") is: The first statement in a basic block, and each subsequent statement after it must be indented by the same amount.
So technically the following Python program is correct:
def perm(l):
# Compute the list of all permutations of l
if len(l) <= 1:
return [l]
r = []
for i in range(len(l)):
s = l[:i] + l[i+1:]
p = perm(s)
for x in p:
r.append(l[i:i+1] + x)
return r
However, as you can probably tell from above, randomly indenting your code makes is extremely hard to read and follow the flow of the program. It's better to be consistent and follow a style.
PEP 8 -- the Python style guide -- says:
Use 4 spaces per indentation level.
That is, each statement that is starting a new block and each subsequent statement in the new block, should be indented four spaces from the current indentation level. Here is the above program indented according to the PEP8 style guide:
def perm(l):
# Compute the list of all permutations of l
if len(l) <= 1:
return [l]
r = []
for i in range(len(l)):
s = l[:i] + l[i+1:]
p = perm(s)
for x in p:
r.append(l[i:i+1] + x)
return r
Can I still use tabs?
Python realizes that some people still prefer tabs over spaces and that legacy code may use tabs rather than spaces, so it allows the use of tabs as indentation. PEP8 touches on this topic:
Spaces are the preferred indentation method.
Tabs should be used solely to remain consistent with code that is already indented with tabs.
Note however the one big caveat is not to use both tabs and spaces for indentation. Doing so can cause all kinds of strange hard to debug indentation errors. Python expands tabs to the next 8th column, but if your editor is set to a tab size of 4 columns, or you you use spaces as well as tabs, you can easily produce indented code that looks fine in your editor, but Python will refuse to run. The Python 3 compiler explicitly rejects any program containing an ambiguous mixture of tabs and spaces, usually by raising a TabError. However, by default, mixing tabs and spaces is still allowed in Python 2, but it is highly recommended not to use this "feature". Use the -t and -tt command line flags to force Python 2 to raise a warning or (preferably) an error respectively. PEP8 also discusses this topic:
Python 3 disallows mixing the use of tabs and spaces for indentation.
Python 2 code indented with a mixture of tabs and spaces should be converted to using spaces exclusively.
When invoking the Python 2 command line interpreter with the -t option, it issues warnings about code that illegally mixes tabs and spaces. When using -tt these warnings become errors. These options are highly recommended!
What does "IndentationError: unexpected indent" mean?
Problem
This error occurs when a statement is unnecessarily indented or its indentation does not match the indentation of former statements in the same block. For example, the first statement in the program below is unnecessarily indented:
>>> print('Hello') # this is indented
File "<stdin>", line 1
print('Hello') # this is indented
^
IndentationError: unexpected indent
In this example, the can_drive = True line in the if block does not match the indentation of any former statement:
>>> age = 10
>>> can_drive = None
>>>
>>> if age >= 18:
... print('You can drive')
... can_drive = True # incorrectly indented
File "<stdin>", line 3
can_drive = True # incorrectly indented
^
IndentationError: unexpected indent
Fix
The fix for this error is to first make sure the problematic line even needs to be indented. For example, the above example using print can be fixed simply be unindenting the line:
>>> print('Hello') # simply unindent the line
Hello
However, if you are sure the line does need to be indented, the indentation needs to match that of a former statement in the same block. In the second example above using if, we can fix the error by making sure the line with can_drive = True is indented at the same level as the former statements in the if body:
>>> age = 10
>>> can_drive = None
>>>
>>> if age >= 18:
... print('You can drive')
... can_drive = True # indent this line at the same level.
...
What does "IndentationError: expected an indented block" mean?
(This might also occur as SyntaxError: unexpected EOF while parsing in Python 3.8 or lower.)
Problem
This error occurs when Python sees the 'header' for a compound statement, such as if <condition>: or while <condition>: but the compound statement's body or block is never defined. For example in the code below we began an if statement, but we never define a body for the statement:
>>> if True:
...
File "<stdin>", line 2
^
IndentationError: expected an indented block
In this second example, we began writing a for loop, but we forget to indent the for loop body. So Python still expects an indented block for the for loop body:
>>> names = ['sarah', 'lucy', 'michael']
>>> for name in names:
... print(name)
File "<stdin>", line 2
print(name)
^
IndentationError: expected an indented block
Comments don't count as bodies:
>>> if True:
... # TODO
...
File "<stdin>", line 3
^
IndentationError: expected an indented block
Fix
The fix for this error is to simply include a body for the compound statement.
As shown above, a common mistake by new users is that they forget to indent the body. If this is the case, make sure each statement meant to be included in the compound statement's body is indented at the same level under the compound statement's beginning. Here is the above example fixed:
>>> names = ['sarah', 'lucy', 'michael']
>>> for name in names:
... print(name) # The for loop body is now correctly indented.
...
sarah
lucy
michael
Another common case is that, for some reason, a user may not want to define an actual body for the compound statement, or the body may be commented out. In this case, the pass statement can be used. The pass statement can be used anywhere Python expects one or more statements as a placeholder. From the documentation for pass:
pass is a null operation — when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed, for example:
def f(arg): pass # a function that does nothing (yet)
class C: pass # a class with no methods (yet)
Here is the above example with the if statement fixed by using the pass keyword:
>>> if True:
... pass # We don't want to define a body.
...
>>>
What does "IndentationError: unindent does not match any outer indentation level" mean?
Problem
This error occurs when you unindent a statement, but now the indentation level of that statement does not match that of any former statement. For example, in the below code we unindent the second call to print. However, the indentation level does not match that of any former statement:
>>> if True:
... if True:
... print('yes')
... print()
File "<stdin>", line 4
print()
^
IndentationError: unindent does not match any outer indentation level
This error is especially hard to catch because even one space will cause your code to fail.
Fix
The fix is to ensure that when you unindent a statement, the indentation level matches that of a former statement. Consider the above example once again. In the example, I want the second call to print to be in the first if statements body. So I need to make sure that that line's indentation level matches that of the former statements in the first if statement's body:
>>> if True:
... if True:
... print('yes')
... print() # indentation level now matches former statement's level.
...
yes
>>>
I'm still getting an IndentationError but my program appears to be correctly indented. What do I do?
If your program visually appears to have correct indentation, but your still getting an IndentationError you have most likely mixed tabs with spaces. This will sometimes cause Python to raises strange errors. See the subsection Special cases under What does "TabError: inconsistent use of tabs and spaces in indentation" mean? for an more in-depth explanation of the problem.
What does "TabError: inconsistent use of tabs and spaces in indentation" mean?
Problem
This error only occurs when you attempt to mix tabs and spaces as indentation characters. As said above, Python will not allow your program to contain a mix of tabs and spaces, and will raise the specific exception TabError if it finds you have. For example, in the program below, a mix of tabs and spaces is used for indentation:
>>> if True:
... if True:
... print()
... print()
... print()
File "<stdin>", line 5
print()
^
TabError: inconsistent use of tabs and spaces in indentation
Here is a picture which visually shows the whitespace in the above program. Gray dots are spaces, and gray arrows are tabs:
We can see we have indeed mixed spaces and tabs for indentation.
Special cases
Note Python will not always raise a TabError if you mix tabs and spaces into your program. If the program indentation is unambiguous, Python will allow tabs and spaces to be mixed. For example:
>>> if True:
... if True: # tab
... pass # tab, then 4 spaces
...
>>>
And sometimes Python simply chokes on the mixture of tabs and spaces and erroneously raises an IndentationError exception when a TabError would be more appropriate. Another example:
>>> if True:
... pass # tab
... pass # 4 spaces
File "<stdin>", line 3
pass # 4 spaces
^
IndentationError: unindent does not match any outer indentation level
As you can see, running your code this way can create mysterious errors. Even though the program visually appears to be fine, Python became confused trying to parse the tabs and spaces used for indention and errored out.
These are excellent examples that demonstrate why to never mix tabs and spaces and make use of the -t and -tt interpreter flags when using Python 2.
Fix
If your program is short, probably the easiest and quickest fix is to simply re-indent the program. Make sure each statement is indented by four spaces per indention level (see How do I indent my code?).
However, if you already have a large program that you've mixed tabs and spaces into, there are automated tools that can be used to convert all of your indentation to just spaces.
Many editors such as PyCharm and SublimeText have options to automatically convert tabs to spaces. There are also several on-line tools such as Tabs To Spaces or Browserling that allow you to quickly re-indent your code. There are also tools written in Python. autopep8 for example can automatically re-indent your code and fix other indentation errors as well.
Even the best tools though will sometimes not be able to fix all of your indentation errors and you'll have to fix them manually. That's why it's important to always properly indent your code from the start.
A note about "SyntaxError" related indentation problems
Although not often, sometimes certain SyntaxError exceptions are raised due to incorrect indentation. For example, look at the code below:
if True:
pass
pass # oops! this statement should be indented!.
else:
pass
When the above code is run, a SyntaxError is raised:
Traceback (most recent call last):
File "python", line 4
else:
^
SyntaxError: invalid syntax
Although Python raises a SyntaxError, the real problem with the above code is that the second pass statement should be indented. Because the second pass isn't indented, Python doesn't realize that the previous if statement and the else statement are meant to be connected.
The fix for this type of error is to simply correctly re-indent your code. To see how to properly indent your code, see the section How do I indent my code?.
I'm still having a hard time with Python's indentation syntax. What do I do?
Don't get discouraged if you're still struggling. It can take time to get use to
Python's whitespace syntax rules. Here are some tips to help:
Get an editor that will tell you when you have an indentation error. Some goods ones are as said above are, PyCharm, SublimeText, and Jupyter Notebook.
When you indent your code, count out loud to yourself how many times you press the space-bar (or tab key). For example, if you needed to indent a line by four spaces, you would say out loud "one, two, three, four" while simultaneously pressing the space-bar each time. It sounds silly, but it helps train your brain to think about how deep you're indenting your code.
If you have an editor, see if it has an option to automatically convert tabs to spaces.
View others' code. Browse github or Stackoverflow and see examples of Python code.
Just write code. That's the single best way to get better. The more you write Python code, the better you'll get.
Resources used
https://en.wikipedia.org/
https://docs.python.org/3/
http://python-history.blogspot.com/2009/02/early-language-design-and-development.html
https://www.python.org/dev/peps/pep-0008/

Sublime Text 3
If it happens that you code in Sublime Text 3, this could help you with indentations problemes
In Sublime Text, while editing a Python file:
Sublime Text menu > Preferences > Settings - Syntax Specific :
Python.sublime-settings
{
"tab_size": 4,
"translate_tabs_to_spaces": true
}

You see, you have a tiny error.
if True:
if False:
print('foo')
print('bar')
You were supposed to do:
if True:
if False:
print('foo')
print('bar')
As you can see your print is only indented 3 spaces, it is supposed to be indented 4 spaces.

Historical note for Python 2
By default, Python 2 allowed tabs and spaces to be mixed, and would not produce an error by default. Passing the -tt option to Python 2.x causes it to raise an exception in the same cases that 3.x does, and -t causes a warning instead. The full details are explained at Python's interpretation of tabs and spaces to indent.
Note in particular that tabs are treated as 8 spaces (rather, they effectively increase the number of perceived spaces up to the next multiple of 8). Thus, if you were displaying the code with a standard 4-space indent, but have mixed spaces and tabs, you could end up with code that satisfies the indentation rules, but is not considered to be indented the same way that it looks.
As a result, you could get all kinds of other errors. For example:
# in 2.x
def example():
def nested(): # suppose this is indented with a tab
x = [1] # and this with two tabs
print x[0] + 1 # but this with 8 spaces instead of a tab
nested()
(Note that Stack Overflow's Markdown rendering will show the indentation as spaces even if I use tabs.)
That gives a NameError, since print x is no longer inside the nested function and x is out of scope in the outer example. Similarly, we could easily create a TypeError by giving example a local x = 1, or ValueError by giving it a local x = [].

Quick checklist
Incorrect indentation most commonly results in IndentationError, but it can also result in TabError (a sub-type of IndentationError) or SyntaxError (the indentation itself was legal, but it caused other code to have a syntax error). Indentation that is valid for Python code, but wrong for the programmer's intent, causes logical errors (the code doesn't raise an exception, but does something wrong).
It is strongly recommended not to use tabs for indentation. In 2.x, running Python with the -tt command line argument causes it to raise the same TabError, which is useful for finding problems.
The community standard, laid out in PEP 8, is to use four spaces per level of indentation.
Statements like if, for, def and class that end with a colon :, need an indented block after them:
if x:
do_y() # <- this must be indented
Blocks cannot be empty. Use the pass statement if nothing should happen:
if x:
pass # this statement does nothing, except make the block non-empty
Code within a block must have the same indentation:
if x:
do_y()
do_z() # this needs to line up with do_y()
The first line of code that lines up with the opening statement, or a lower level of indentation, is outside the block:
if x:
do_y()
do_z() # this happens regardless of the x value
# cannot write `else`: here; that is a syntax error
for i in range(10):
if x:
do_y()
do_z() # both the `if` and `for` blocks are ended
Python interprets tabs as expanding to the next 8th column; but in 3.x, indentation that mixes spaces and tabs must have the exact same pattern to count as the same indentation (and to indent further requires having the same pattern as a prefix). Failure to get this right results in TabError.
while and for loops in Python may have an else clause, which executes if the loop complete normally rather than via break. This is a common source of logical errors:
for i in range(10):
if i % 2:
print(f'{i} is odd')
else: # wrongly indented
print(f'{i} is even') # only happens once, and claims 9 is even!

Quick fix for Sublime users:
Press Ctrl-H to access Find and Replace
In Find: Type 4 spaces
In Replace: Copy and paste a tab from somewhere in your code
Click Replace All

"def listening(self,phrases=None):" Eror in python [duplicate]

I have a Python script:
if True:
if False:
print('foo')
print('bar')
However, when I attempt to run my script, Python raises an IndentationError:
File "script.py", line 4
print('bar')
^
IndentationError: unindent does not match any outer indentation level
I kept playing around with my program, and I was able to produce four errors in total:
IndentationError: unexpected indent
IndentationError: expected an indented block
TabError: inconsistent use of tabs and spaces in indentation
IndentationError: unindent does not match any outer indentation level
What do these errors mean? What am I doing wrong? How can I fix my code?
Note: This is an attempt at a canonical question because I see many similar posts every month. This is not a duplicate of existing questions about unindents or unexpected indents because they only deal with one type of indentation error each, and I'm looking to cover them all in one place.
It's also possible to have logically incorrect indentation that does not cause an error message. One common form of this is attaching else: to a for or while loop rather than (as intended) the corresponding if:. See Else clause on Python while statement if you need to close questions where OP did that.

Why does indentation matter?
In Python, indentation is used to delimit blocks of code. This is different from many other languages that use curly braces {} to delimit blocks such as Java, Javascript, and C. Because of this, Python users must pay close attention to when and how they indent their code because whitespace matters.
When Python encounters a problem with the indentation of your program, it either raises an exception called IndentationError or TabError.
A little history
The historical reasons for why Python uses indentation vs the arguably more commonly accepted curly braces {} is outlined in an article of the history of Python by Guido van Rossum - the creator of Python:
Python’s use of indentation comes directly from ABC, but this idea didn’t originate with ABC--it had already been promoted by Donald Knuth and was a well-known concept of programming style. (The occam programming language also used it.) However, ABC’s authors did invent the use of the colon that separates the lead-in clause from the indented block. After early user testing without the colon, it was discovered that the meaning of the indentation was unclear to beginners being taught the first steps of programming. The addition of the colon clarified it significantly: the colon somehow draws attention to what follows and ties the phrases before and after it together in just the right way.
How do I indent my code?
The basic rule for indenting Python code (considering that you treat the entire program as a "basic block") is: The first statement in a basic block, and each subsequent statement after it must be indented by the same amount.
So technically the following Python program is correct:
def perm(l):
# Compute the list of all permutations of l
if len(l) <= 1:
return [l]
r = []
for i in range(len(l)):
s = l[:i] + l[i+1:]
p = perm(s)
for x in p:
r.append(l[i:i+1] + x)
return r
However, as you can probably tell from above, randomly indenting your code makes is extremely hard to read and follow the flow of the program. It's better to be consistent and follow a style.
PEP 8 -- the Python style guide -- says:
Use 4 spaces per indentation level.
That is, each statement that is starting a new block and each subsequent statement in the new block, should be indented four spaces from the current indentation level. Here is the above program indented according to the PEP8 style guide:
def perm(l):
# Compute the list of all permutations of l
if len(l) <= 1:
return [l]
r = []
for i in range(len(l)):
s = l[:i] + l[i+1:]
p = perm(s)
for x in p:
r.append(l[i:i+1] + x)
return r
Can I still use tabs?
Python realizes that some people still prefer tabs over spaces and that legacy code may use tabs rather than spaces, so it allows the use of tabs as indentation. PEP8 touches on this topic:
Spaces are the preferred indentation method.
Tabs should be used solely to remain consistent with code that is already indented with tabs.
Note however the one big caveat is not to use both tabs and spaces for indentation. Doing so can cause all kinds of strange hard to debug indentation errors. Python expands tabs to the next 8th column, but if your editor is set to a tab size of 4 columns, or you you use spaces as well as tabs, you can easily produce indented code that looks fine in your editor, but Python will refuse to run. The Python 3 compiler explicitly rejects any program containing an ambiguous mixture of tabs and spaces, usually by raising a TabError. However, by default, mixing tabs and spaces is still allowed in Python 2, but it is highly recommended not to use this "feature". Use the -t and -tt command line flags to force Python 2 to raise a warning or (preferably) an error respectively. PEP8 also discusses this topic:
Python 3 disallows mixing the use of tabs and spaces for indentation.
Python 2 code indented with a mixture of tabs and spaces should be converted to using spaces exclusively.
When invoking the Python 2 command line interpreter with the -t option, it issues warnings about code that illegally mixes tabs and spaces. When using -tt these warnings become errors. These options are highly recommended!
What does "IndentationError: unexpected indent" mean?
Problem
This error occurs when a statement is unnecessarily indented or its indentation does not match the indentation of former statements in the same block. For example, the first statement in the program below is unnecessarily indented:
>>> print('Hello') # this is indented
File "<stdin>", line 1
print('Hello') # this is indented
^
IndentationError: unexpected indent
In this example, the can_drive = True line in the if block does not match the indentation of any former statement:
>>> age = 10
>>> can_drive = None
>>>
>>> if age >= 18:
... print('You can drive')
... can_drive = True # incorrectly indented
File "<stdin>", line 3
can_drive = True # incorrectly indented
^
IndentationError: unexpected indent
Fix
The fix for this error is to first make sure the problematic line even needs to be indented. For example, the above example using print can be fixed simply be unindenting the line:
>>> print('Hello') # simply unindent the line
Hello
However, if you are sure the line does need to be indented, the indentation needs to match that of a former statement in the same block. In the second example above using if, we can fix the error by making sure the line with can_drive = True is indented at the same level as the former statements in the if body:
>>> age = 10
>>> can_drive = None
>>>
>>> if age >= 18:
... print('You can drive')
... can_drive = True # indent this line at the same level.
...
What does "IndentationError: expected an indented block" mean?
(This might also occur as SyntaxError: unexpected EOF while parsing in Python 3.8 or lower.)
Problem
This error occurs when Python sees the 'header' for a compound statement, such as if <condition>: or while <condition>: but the compound statement's body or block is never defined. For example in the code below we began an if statement, but we never define a body for the statement:
>>> if True:
...
File "<stdin>", line 2
^
IndentationError: expected an indented block
In this second example, we began writing a for loop, but we forget to indent the for loop body. So Python still expects an indented block for the for loop body:
>>> names = ['sarah', 'lucy', 'michael']
>>> for name in names:
... print(name)
File "<stdin>", line 2
print(name)
^
IndentationError: expected an indented block
Comments don't count as bodies:
>>> if True:
... # TODO
...
File "<stdin>", line 3
^
IndentationError: expected an indented block
Fix
The fix for this error is to simply include a body for the compound statement.
As shown above, a common mistake by new users is that they forget to indent the body. If this is the case, make sure each statement meant to be included in the compound statement's body is indented at the same level under the compound statement's beginning. Here is the above example fixed:
>>> names = ['sarah', 'lucy', 'michael']
>>> for name in names:
... print(name) # The for loop body is now correctly indented.
...
sarah
lucy
michael
Another common case is that, for some reason, a user may not want to define an actual body for the compound statement, or the body may be commented out. In this case, the pass statement can be used. The pass statement can be used anywhere Python expects one or more statements as a placeholder. From the documentation for pass:
pass is a null operation — when it is executed, nothing happens. It is useful as a placeholder when a statement is required syntactically, but no code needs to be executed, for example:
def f(arg): pass # a function that does nothing (yet)
class C: pass # a class with no methods (yet)
Here is the above example with the if statement fixed by using the pass keyword:
>>> if True:
... pass # We don't want to define a body.
...
>>>
What does "IndentationError: unindent does not match any outer indentation level" mean?
Problem
This error occurs when you unindent a statement, but now the indentation level of that statement does not match that of any former statement. For example, in the below code we unindent the second call to print. However, the indentation level does not match that of any former statement:
>>> if True:
... if True:
... print('yes')
... print()
File "<stdin>", line 4
print()
^
IndentationError: unindent does not match any outer indentation level
This error is especially hard to catch because even one space will cause your code to fail.
Fix
The fix is to ensure that when you unindent a statement, the indentation level matches that of a former statement. Consider the above example once again. In the example, I want the second call to print to be in the first if statements body. So I need to make sure that that line's indentation level matches that of the former statements in the first if statement's body:
>>> if True:
... if True:
... print('yes')
... print() # indentation level now matches former statement's level.
...
yes
>>>
I'm still getting an IndentationError but my program appears to be correctly indented. What do I do?
If your program visually appears to have correct indentation, but your still getting an IndentationError you have most likely mixed tabs with spaces. This will sometimes cause Python to raises strange errors. See the subsection Special cases under What does "TabError: inconsistent use of tabs and spaces in indentation" mean? for an more in-depth explanation of the problem.
What does "TabError: inconsistent use of tabs and spaces in indentation" mean?
Problem
This error only occurs when you attempt to mix tabs and spaces as indentation characters. As said above, Python will not allow your program to contain a mix of tabs and spaces, and will raise the specific exception TabError if it finds you have. For example, in the program below, a mix of tabs and spaces is used for indentation:
>>> if True:
... if True:
... print()
... print()
... print()
File "<stdin>", line 5
print()
^
TabError: inconsistent use of tabs and spaces in indentation
Here is a picture which visually shows the whitespace in the above program. Gray dots are spaces, and gray arrows are tabs:
We can see we have indeed mixed spaces and tabs for indentation.
Special cases
Note Python will not always raise a TabError if you mix tabs and spaces into your program. If the program indentation is unambiguous, Python will allow tabs and spaces to be mixed. For example:
>>> if True:
... if True: # tab
... pass # tab, then 4 spaces
...
>>>
And sometimes Python simply chokes on the mixture of tabs and spaces and erroneously raises an IndentationError exception when a TabError would be more appropriate. Another example:
>>> if True:
... pass # tab
... pass # 4 spaces
File "<stdin>", line 3
pass # 4 spaces
^
IndentationError: unindent does not match any outer indentation level
As you can see, running your code this way can create mysterious errors. Even though the program visually appears to be fine, Python became confused trying to parse the tabs and spaces used for indention and errored out.
These are excellent examples that demonstrate why to never mix tabs and spaces and make use of the -t and -tt interpreter flags when using Python 2.
Fix
If your program is short, probably the easiest and quickest fix is to simply re-indent the program. Make sure each statement is indented by four spaces per indention level (see How do I indent my code?).
However, if you already have a large program that you've mixed tabs and spaces into, there are automated tools that can be used to convert all of your indentation to just spaces.
Many editors such as PyCharm and SublimeText have options to automatically convert tabs to spaces. There are also several on-line tools such as Tabs To Spaces or Browserling that allow you to quickly re-indent your code. There are also tools written in Python. autopep8 for example can automatically re-indent your code and fix other indentation errors as well.
Even the best tools though will sometimes not be able to fix all of your indentation errors and you'll have to fix them manually. That's why it's important to always properly indent your code from the start.
A note about "SyntaxError" related indentation problems
Although not often, sometimes certain SyntaxError exceptions are raised due to incorrect indentation. For example, look at the code below:
if True:
pass
pass # oops! this statement should be indented!.
else:
pass
When the above code is run, a SyntaxError is raised:
Traceback (most recent call last):
File "python", line 4
else:
^
SyntaxError: invalid syntax
Although Python raises a SyntaxError, the real problem with the above code is that the second pass statement should be indented. Because the second pass isn't indented, Python doesn't realize that the previous if statement and the else statement are meant to be connected.
The fix for this type of error is to simply correctly re-indent your code. To see how to properly indent your code, see the section How do I indent my code?.
I'm still having a hard time with Python's indentation syntax. What do I do?
Don't get discouraged if you're still struggling. It can take time to get use to
Python's whitespace syntax rules. Here are some tips to help:
Get an editor that will tell you when you have an indentation error. Some goods ones are as said above are, PyCharm, SublimeText, and Jupyter Notebook.
When you indent your code, count out loud to yourself how many times you press the space-bar (or tab key). For example, if you needed to indent a line by four spaces, you would say out loud "one, two, three, four" while simultaneously pressing the space-bar each time. It sounds silly, but it helps train your brain to think about how deep you're indenting your code.
If you have an editor, see if it has an option to automatically convert tabs to spaces.
View others' code. Browse github or Stackoverflow and see examples of Python code.
Just write code. That's the single best way to get better. The more you write Python code, the better you'll get.
Resources used
https://en.wikipedia.org/
https://docs.python.org/3/
http://python-history.blogspot.com/2009/02/early-language-design-and-development.html
https://www.python.org/dev/peps/pep-0008/

Sublime Text 3
If it happens that you code in Sublime Text 3, this could help you with indentations problemes
In Sublime Text, while editing a Python file:
Sublime Text menu > Preferences > Settings - Syntax Specific :
Python.sublime-settings
{
"tab_size": 4,
"translate_tabs_to_spaces": true
}

You see, you have a tiny error.
if True:
if False:
print('foo')
print('bar')
You were supposed to do:
if True:
if False:
print('foo')
print('bar')
As you can see your print is only indented 3 spaces, it is supposed to be indented 4 spaces.

Historical note for Python 2
By default, Python 2 allowed tabs and spaces to be mixed, and would not produce an error by default. Passing the -tt option to Python 2.x causes it to raise an exception in the same cases that 3.x does, and -t causes a warning instead. The full details are explained at Python's interpretation of tabs and spaces to indent.
Note in particular that tabs are treated as 8 spaces (rather, they effectively increase the number of perceived spaces up to the next multiple of 8). Thus, if you were displaying the code with a standard 4-space indent, but have mixed spaces and tabs, you could end up with code that satisfies the indentation rules, but is not considered to be indented the same way that it looks.
As a result, you could get all kinds of other errors. For example:
# in 2.x
def example():
def nested(): # suppose this is indented with a tab
x = [1] # and this with two tabs
print x[0] + 1 # but this with 8 spaces instead of a tab
nested()
(Note that Stack Overflow's Markdown rendering will show the indentation as spaces even if I use tabs.)
That gives a NameError, since print x is no longer inside the nested function and x is out of scope in the outer example. Similarly, we could easily create a TypeError by giving example a local x = 1, or ValueError by giving it a local x = [].

Quick checklist
Incorrect indentation most commonly results in IndentationError, but it can also result in TabError (a sub-type of IndentationError) or SyntaxError (the indentation itself was legal, but it caused other code to have a syntax error). Indentation that is valid for Python code, but wrong for the programmer's intent, causes logical errors (the code doesn't raise an exception, but does something wrong).
It is strongly recommended not to use tabs for indentation. In 2.x, running Python with the -tt command line argument causes it to raise the same TabError, which is useful for finding problems.
The community standard, laid out in PEP 8, is to use four spaces per level of indentation.
Statements like if, for, def and class that end with a colon :, need an indented block after them:
if x:
do_y() # <- this must be indented
Blocks cannot be empty. Use the pass statement if nothing should happen:
if x:
pass # this statement does nothing, except make the block non-empty
Code within a block must have the same indentation:
if x:
do_y()
do_z() # this needs to line up with do_y()
The first line of code that lines up with the opening statement, or a lower level of indentation, is outside the block:
if x:
do_y()
do_z() # this happens regardless of the x value
# cannot write `else`: here; that is a syntax error
for i in range(10):
if x:
do_y()
do_z() # both the `if` and `for` blocks are ended
Python interprets tabs as expanding to the next 8th column; but in 3.x, indentation that mixes spaces and tabs must have the exact same pattern to count as the same indentation (and to indent further requires having the same pattern as a prefix). Failure to get this right results in TabError.
while and for loops in Python may have an else clause, which executes if the loop complete normally rather than via break. This is a common source of logical errors:
for i in range(10):
if i % 2:
print(f'{i} is odd')
else: # wrongly indented
print(f'{i} is even') # only happens once, and claims 9 is even!

Quick fix for Sublime users:
Press Ctrl-H to access Find and Replace
In Find: Type 4 spaces
In Replace: Copy and paste a tab from somewhere in your code
Click Replace All

SpeechRecognition as a function [duplicate]

When I compile the Python code below, I get
IndentationError: unindent does not match any outer indentation level
import sys
def Factorial(n): # Return factorial
result = 1
for i in range (1,n):
result = result * i
print "factorial is ",result
return result
Why?

Other posters are probably correct...there might be spaces mixed in with your tabs. Try doing a search & replace to replace all tabs with a few spaces.
Try this:
import sys
def Factorial(n): # return factorial
result = 1
for i in range (1,n):
result = result * i
print "factorial is ",result
return result
print Factorial(10)

IMPORTANT:
Spaces are the preferred method - see PEP 8 Indentation and Tabs or Spaces?. (Thanks to #Siha for this.)
For Sublime Text users:
Set Sublime Text to use tabs for indentation:
View --> Indentation --> Convert Indentation to Tabs
Uncheck the Indent Using Spaces option as well in the same sub-menu above.
This will immediately resolve this issue.

To easily check for problems with tabs/spaces you can actually do this:
python -m tabnanny yourfile.py
or you can just set up your editor correctly of course :-)

Are you sure you are not mixing tabs and spaces in your indentation white space? (That will cause that error.)
Note, it is recommended that you don't use tabs in Python code. See the style guide. You should configure Notepad++ to insert spaces for tabs.

Whenever I've encountered this error, it's because I've somehow mixed up tabs and spaces in my editor.

If you are using Vim, hit escape and then type
gg=G
This auto indents everything and will clear up any spaces you have thrown in.

If you use Python's IDLE editor you can do as it suggests in one of similar error messages:
1) select all, e.g. Ctrl + A
2) Go to Format -> Untabify Region
3) Double check your indenting is still correct, save and rerun your program.
I'm using Python 2.5.4

The line: result = result * i should be indented (it is the body of the for-loop).
Or - you have mixed space and tab characters

For Spyder users goto
Source > Fix Indentation
to fix the issue immediately

Using Visual studio code
If you are using vs code than, it will convert all mix Indentation to either space or tabs using this simple steps below.
press Ctrl + Shift + p
type indent using spaces
Press Enter

On Atom
go to
Packages > Whitespace > Convert Spaces to Tabs
Then check again your file indentation:
python -m tabnanny yourFile.py
or
>python
>>> help("yourFile.py")

If you use notepad++, do a "replace" with extended search mode to find \t and replace with four spaces.

Looks to be an indentation problem. You don't have to match curly brackets in Python but you do have to match indentation levels.
The best way to prevent space/tab problems is to display invisible characters within your text editor. This will give you a quick way to prevent and/or resolve indentation-related errors.
Also, injecting copy-pasted code is a common source for this type of problem.

If you use colab, then you can do avoid the error by this commands.
< Ctrl-A >
< Tab >
< Shift-Tab >
It's all [tab] indentation convert to [space] indentation. Then OK.

Just a addition. I had a similar problem with the both indentations in Notepad++.
Unexcepted indentation
Outer Indentation Level
Go to ----> Search tab ----> tap on replace ----> hit the radio button Extended below ---> Now replace \t with four spaces
Go to ----> Search tab ----> tap on replace ----> hit the radio button Extended below ---> Now replace \n with nothing

I was using Jupyter notebook and tried almost all of the above solutions (adapting to my scenario) to no use. I then went line by line, deleted all spaces for each line and replaced with tab. That solved the issue.

For what its worth, my docstring was indented too much and this also throws the same error
class junk:
"""docstring is indented too much"""
def fun(): return
IndentationError: unindent does not match any outer indentation level

I'm using Sublime text in Ubuntu OS. To fix this issue go to
view -> Indentation -> convert indentation to tabs

It could be because the function above it is not indented the same way.
i.e.
class a:
def blah:
print("Hello world")
def blah1:
print("Hello world")

Since I realize there's no answer specific to spyder,I'll add one:
Basically, carefully look at your if statement and make sure all if, elif and else have the same spacing that is they're in the same line at the start like so:
def your_choice(answer):
if answer>5:
print("You're overaged")
elif answer<=5 and answer>1:
print("Welcome to the toddler's club!")
else:
print("No worries mate!")

I am using Sublime Text 3 with a Flask project. I fixed the error using View > Indentation > Tab Width: 4 after unselected Indent Using Spaces

This is because there is a mix-up of both tabs and spaces.
You can either remove all the spaces and replace them with tabs.
Or,
Try writing this:
#!/usr/bin/python -tt
at the beginning of the code. This line resolves any differences between tabs and spaces.

I had the same issue yesterday, it was indentation error, was using sublime text editor. took my hours trying to fix it and at the end I ended up copying the code into VI text editor and it just worked fine. ps python is too whitespace sensitive, make sure not to mix space and tab.

for Atom Users, Packages ->whitspace -> remove trailing whitespaces
this worked for me

I had a function defined, but it did not had any content apart from its function comments...
def foo(bar):
# Some awesome temporary comment.
# But there is actually nothing in the function!
# D'Oh!
It yelled :
File "foobar.py", line 69
^
IndentationError: expected an indented block
(note that the line the ^ mark points to is empty)
--
Multiple solutions:
1: Just comment out the function
2: Add function comment
def foo(bar):
'' Some awesome comment. This comment could be just one space.''
3: Add line that does nothing
def foo(bar):
0
In any case, make sure to make it obvious why it is an empty function - for yourself, or for your peers that will use your code

Firstly, just to remind you there is a logical error you better keep result=1 or else your output will be result=0 even after the loop runs.
Secondly you can write it like this:
import sys
def Factorial(n): # Return factorial
result = 0
for i in range (1,n):
result = result * i
print "factorial is ",result
return result
Leaving a line will tell the python shell that the FOR statements have ended. If you have experience using the python shell then you can understand why we have to leave a line.

For example:
1. def convert_distance(miles):
2. km = miles * 1.6
3. return km
In this code same situation occurred for me. Just delete the previous indent spaces of
line 2 and 3, and then either use tab or space. Never use both. Give proper indentation while writing code in python.
For Spyder goto Source > Fix Indentation. Same goes to VC Code and sublime text or any other editor. Fix the indentation.

I got this error even though I didn't have any tabs in my code, and the reason was there was a superfluous closing parenthesis somewhere in my code. I should have figured this out earlier because it was messing up spaces before and after some equal signs... If you find anything off even after running Reformat code in your IDE (or manually running autopep8), make sure all your parentheses match, starting backwards from the weird spaces before/after the first equals sign.

I had the same error because of another thing, it was not about tabs vs. spaces. I had the first if slightly more indented than an else: much further down. If it is just about a space or two, you might oversee it after a long code block. Same thing with docstrings:
"""comment comment
comment
"""
They also need to be aligned, see the other answer on the same page here.
Reproducible with a few lines:
if a==1:
print('test')
else:
print('test2')
Throws:
File "<ipython-input-127-52bbac35ad7d>", line 3
else:
^
IndentationError: unindent does not match any outer indentation level

I actually get this in pylint from a bracket in the wrong place.
I'm adding this answer because I sent a lot of time looking for tabs.
In this case, it has nothing to do with tabs or spaces.
def some_instance_function(self):
json_response = self.some_other_function()
def compare_result(json_str, variable):
"""
Sub function for comparison
"""
json_value = self.json_response.get(json_str, f"{json_str} not found")
if str(json_value) != str(variable):
logging.error("Error message: %s, %s",
json_value,
variable) # <-- Putting the bracket here causes the error below
#) <-- Moving the bracket here fixes the issue
return False
return True
logging.debug("Response: %s", self.json_response)
# ^----The pylint error reports here