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While asking this question, I realized I didn't know much about raw strings. For somebody claiming to be a Django trainer, this sucks.
I know what an encoding is, and I know what u'' alone does since I get what is Unicode.
But what does r'' do exactly? What kind of string does it result in?
And above all, what the heck does ur'' do?
Finally, is there any reliable way to go back from a Unicode string to a simple raw string?
Ah, and by the way, if your system and your text editor charset are set to UTF-8, does u'' actually do anything?
There's not really any "raw string"; there are raw string literals, which are exactly the string literals marked by an 'r' before the opening quote.
A "raw string literal" is a slightly different syntax for a string literal, in which a backslash, \, is taken as meaning "just a backslash" (except when it comes right before a quote that would otherwise terminate the literal) -- no "escape sequences" to represent newlines, tabs, backspaces, form-feeds, and so on. In normal string literals, each backslash must be doubled up to avoid being taken as the start of an escape sequence.
This syntax variant exists mostly because the syntax of regular expression patterns is heavy with backslashes (but never at the end, so the "except" clause above doesn't matter) and it looks a bit better when you avoid doubling up each of them -- that's all. It also gained some popularity to express native Windows file paths (with backslashes instead of regular slashes like on other platforms), but that's very rarely needed (since normal slashes mostly work fine on Windows too) and imperfect (due to the "except" clause above).
r'...' is a byte string (in Python 2.*), ur'...' is a Unicode string (again, in Python 2.*), and any of the other three kinds of quoting also produces exactly the same types of strings (so for example r'...', r'''...''', r"...", r"""...""" are all byte strings, and so on).
Not sure what you mean by "going back" - there is no intrinsically back and forward directions, because there's no raw string type, it's just an alternative syntax to express perfectly normal string objects, byte or unicode as they may be.
And yes, in Python 2.*, u'...' is of course always distinct from just '...' -- the former is a unicode string, the latter is a byte string. What encoding the literal might be expressed in is a completely orthogonal issue.
E.g., consider (Python 2.6):
>>> sys.getsizeof('ciao')
28
>>> sys.getsizeof(u'ciao')
34
The Unicode object of course takes more memory space (very small difference for a very short string, obviously ;-).
There are two types of string in Python 2: the traditional str type and the newer unicode type. If you type a string literal without the u in front you get the old str type which stores 8-bit characters, and with the u in front you get the newer unicode type that can store any Unicode character.
The r doesn't change the type at all, it just changes how the string literal is interpreted. Without the r, backslashes are treated as escape characters. With the r, backslashes are treated as literal. Either way, the type is the same.
ur is of course a Unicode string where backslashes are literal backslashes, not part of escape codes.
You can try to convert a Unicode string to an old string using the str() function, but if there are any unicode characters that cannot be represented in the old string, you will get an exception. You could replace them with question marks first if you wish, but of course this would cause those characters to be unreadable. It is not recommended to use the str type if you want to correctly handle unicode characters.
'raw string' means it is stored as it appears. For example, '\' is just a backslash instead of an escaping.
Let me explain it simply:
In python 2, you can store string in 2 different types.
The first one is ASCII which is str type in python, it uses 1 byte of memory. (256 characters, will store mostly English alphabets and simple symbols)
The 2nd type is UNICODE which is unicode type in python. Unicode stores all types of languages.
By default, python will prefer str type but if you want to store string in unicode type you can put u in front of the text like u'text' or you can do this by calling unicode('text')
So u is just a short way to call a function to cast str to unicode. That's it!
Now the r part, you put it in front of the text to tell the computer that the text is raw text, backslash should not be an escaping character. r'\n' will not create a new line character. It's just plain text containing 2 characters.
If you want to convert str to unicode and also put raw text in there, use ur because ru will raise an error.
NOW, the important part:
You cannot store one backslash by using r, it's the only exception.
So this code will produce error: r'\'
To store a backslash (only one) you need to use '\\'
If you want to store more than 1 characters you can still use r like r'\\' will produce 2 backslashes as you expected.
I don't know the reason why r doesn't work with one backslash storage but the reason isn't described by anyone yet. I hope that it is a bug.
A "u" prefix denotes the value has type unicode rather than str.
Raw string literals, with an "r" prefix, escape any escape sequences within them, so len(r"\n") is 2. Because they escape escape sequences, you cannot end a string literal with a single backslash: that's not a valid escape sequence (e.g. r"\").
"Raw" is not part of the type, it's merely one way to represent the value. For example, "\\n" and r"\n" are identical values, just like 32, 0x20, and 0b100000 are identical.
You can have unicode raw string literals:
>>> u = ur"\n"
>>> print type(u), len(u)
<type 'unicode'> 2
The source file encoding just determines how to interpret the source file, it doesn't affect expressions or types otherwise. However, it's recommended to avoid code where an encoding other than ASCII would change the meaning:
Files using ASCII (or UTF-8, for Python 3.0) should not have a coding cookie. Latin-1 (or UTF-8) should only be used when a comment or docstring needs to mention an author name that requires Latin-1; otherwise, using \x, \u or \U escapes is the preferred way to include non-ASCII data in string literals.
Unicode string literals
Unicode string literals (string literals prefixed by u) are no longer used in Python 3. They are still valid but just for compatibility purposes with Python 2.
Raw string literals
If you want to create a string literal consisting of only easily typable characters like english letters or numbers, you can simply type them: 'hello world'. But if you want to include also some more exotic characters, you'll have to use some workaround.
One of the workarounds are Escape sequences. This way you can for example represent a new line in your string simply by adding two easily typable characters \n to your string literal. So when you print the 'hello\nworld' string, the words will be printed on separate lines. That's very handy!
On the other hand, sometimes you might want to include the actual characters \ and n into your string – you might not want them to be interpreted as a new line. Look at these examples:
'New updates are ready in c:\windows\updates\new'
'In this lesson we will learn what the \n escape sequence does.'
In such situations you can just prefix the string literal with the r character like this: r'hello\nworld' and no escape sequences will be interpreted by Python. The string will be printed exactly as you created it.
Raw string literals are not completely "raw"?
Many people expect the raw string literals to be raw in a sense that "anything placed between the quotes is ignored by Python". That is not true. Python still recognizes all the escape sequences, it just does not interpret them - it leaves them unchanged instead. It means that raw string literals still have to be valid string literals.
From the lexical definition of a string literal:
string ::= "'" stringitem* "'"
stringitem ::= stringchar | escapeseq
stringchar ::= <any source character except "\" or newline or the quote>
escapeseq ::= "\" <any source character>
It is clear that string literals (raw or not) containing a bare quote character: 'hello'world' or ending with a backslash: 'hello world\' are not valid.
Maybe this is obvious, maybe not, but you can make the string '\' by calling x=chr(92)
x=chr(92)
print type(x), len(x) # <type 'str'> 1
y='\\'
print type(y), len(y) # <type 'str'> 1
x==y # True
x is y # False
Hi I have the following data (abstracted) that comes from an API.
"Product" : "T\u00e1bua 21X40"
I'm using the following code to decode the data byte:
var = json.loads(cleanhtml(str(json.dumps(response.content.decode('utf-8')))))
The cleanhtml is a regex function that I've created to remove html tags from the returned data (It's working correctly). Although, decode(utf-8) is not removing characters like \u00e1. My expected output is:
"Product" : "Tábua 21X40"
I've tried to use replace("\\u00e1", "á") but with no success. How can I replace this type of character and what type of character is this?
\u00e1 is another way of representing the á character when displaying the contents of a Python string.
If you open a Python interactive session and run print({"Product" : "T\u00e1bua 21X40"}) you'll see output of {'Product': 'Tábua 21X40'}. The \u00e1 doesn't exist in the string as those individual characters.
The \u escape sequence indicates that the following numbers specify a Unicode character.
Attempting to replace \u00e1 with á won't achieve anything because that's what it already is. Additionally, replace("\\u00e1", "á") is attempting to replace the individual characters of a slash, a u, etc and, as mentioned, they don't actually exist in the string in that way.
If you explain the problem you're encountering further then we may be able to help more, but currently it sounds like the string has the correct content but is just being displayed differently than you expect.
what type of character is this
Here
"Product" : "T\u00e1bua 21X40"
you might observe \u escape sequence, it is followed by 4 hex digits: 00e1, note that this is different represenation of same character, so
print("\u00e1" == "á")
output
True
These type of characters are called character entities. There are different types of entities and this is JSON entity. For demonstration, enter your string here and click unescape.
For your question, if you are using python then you can solve the issue by importing json module. Then you have to decode it as follows.
import json
string = json.loads('"T\u00e1bua 21X40"')
print(string)
While asking this question, I realized I didn't know much about raw strings. For somebody claiming to be a Django trainer, this sucks.
I know what an encoding is, and I know what u'' alone does since I get what is Unicode.
But what does r'' do exactly? What kind of string does it result in?
And above all, what the heck does ur'' do?
Finally, is there any reliable way to go back from a Unicode string to a simple raw string?
Ah, and by the way, if your system and your text editor charset are set to UTF-8, does u'' actually do anything?
There's not really any "raw string"; there are raw string literals, which are exactly the string literals marked by an 'r' before the opening quote.
A "raw string literal" is a slightly different syntax for a string literal, in which a backslash, \, is taken as meaning "just a backslash" (except when it comes right before a quote that would otherwise terminate the literal) -- no "escape sequences" to represent newlines, tabs, backspaces, form-feeds, and so on. In normal string literals, each backslash must be doubled up to avoid being taken as the start of an escape sequence.
This syntax variant exists mostly because the syntax of regular expression patterns is heavy with backslashes (but never at the end, so the "except" clause above doesn't matter) and it looks a bit better when you avoid doubling up each of them -- that's all. It also gained some popularity to express native Windows file paths (with backslashes instead of regular slashes like on other platforms), but that's very rarely needed (since normal slashes mostly work fine on Windows too) and imperfect (due to the "except" clause above).
r'...' is a byte string (in Python 2.*), ur'...' is a Unicode string (again, in Python 2.*), and any of the other three kinds of quoting also produces exactly the same types of strings (so for example r'...', r'''...''', r"...", r"""...""" are all byte strings, and so on).
Not sure what you mean by "going back" - there is no intrinsically back and forward directions, because there's no raw string type, it's just an alternative syntax to express perfectly normal string objects, byte or unicode as they may be.
And yes, in Python 2.*, u'...' is of course always distinct from just '...' -- the former is a unicode string, the latter is a byte string. What encoding the literal might be expressed in is a completely orthogonal issue.
E.g., consider (Python 2.6):
>>> sys.getsizeof('ciao')
28
>>> sys.getsizeof(u'ciao')
34
The Unicode object of course takes more memory space (very small difference for a very short string, obviously ;-).
There are two types of string in Python 2: the traditional str type and the newer unicode type. If you type a string literal without the u in front you get the old str type which stores 8-bit characters, and with the u in front you get the newer unicode type that can store any Unicode character.
The r doesn't change the type at all, it just changes how the string literal is interpreted. Without the r, backslashes are treated as escape characters. With the r, backslashes are treated as literal. Either way, the type is the same.
ur is of course a Unicode string where backslashes are literal backslashes, not part of escape codes.
You can try to convert a Unicode string to an old string using the str() function, but if there are any unicode characters that cannot be represented in the old string, you will get an exception. You could replace them with question marks first if you wish, but of course this would cause those characters to be unreadable. It is not recommended to use the str type if you want to correctly handle unicode characters.
'raw string' means it is stored as it appears. For example, '\' is just a backslash instead of an escaping.
Let me explain it simply:
In python 2, you can store string in 2 different types.
The first one is ASCII which is str type in python, it uses 1 byte of memory. (256 characters, will store mostly English alphabets and simple symbols)
The 2nd type is UNICODE which is unicode type in python. Unicode stores all types of languages.
By default, python will prefer str type but if you want to store string in unicode type you can put u in front of the text like u'text' or you can do this by calling unicode('text')
So u is just a short way to call a function to cast str to unicode. That's it!
Now the r part, you put it in front of the text to tell the computer that the text is raw text, backslash should not be an escaping character. r'\n' will not create a new line character. It's just plain text containing 2 characters.
If you want to convert str to unicode and also put raw text in there, use ur because ru will raise an error.
NOW, the important part:
You cannot store one backslash by using r, it's the only exception.
So this code will produce error: r'\'
To store a backslash (only one) you need to use '\\'
If you want to store more than 1 characters you can still use r like r'\\' will produce 2 backslashes as you expected.
I don't know the reason why r doesn't work with one backslash storage but the reason isn't described by anyone yet. I hope that it is a bug.
A "u" prefix denotes the value has type unicode rather than str.
Raw string literals, with an "r" prefix, escape any escape sequences within them, so len(r"\n") is 2. Because they escape escape sequences, you cannot end a string literal with a single backslash: that's not a valid escape sequence (e.g. r"\").
"Raw" is not part of the type, it's merely one way to represent the value. For example, "\\n" and r"\n" are identical values, just like 32, 0x20, and 0b100000 are identical.
You can have unicode raw string literals:
>>> u = ur"\n"
>>> print type(u), len(u)
<type 'unicode'> 2
The source file encoding just determines how to interpret the source file, it doesn't affect expressions or types otherwise. However, it's recommended to avoid code where an encoding other than ASCII would change the meaning:
Files using ASCII (or UTF-8, for Python 3.0) should not have a coding cookie. Latin-1 (or UTF-8) should only be used when a comment or docstring needs to mention an author name that requires Latin-1; otherwise, using \x, \u or \U escapes is the preferred way to include non-ASCII data in string literals.
Unicode string literals
Unicode string literals (string literals prefixed by u) are no longer used in Python 3. They are still valid but just for compatibility purposes with Python 2.
Raw string literals
If you want to create a string literal consisting of only easily typable characters like english letters or numbers, you can simply type them: 'hello world'. But if you want to include also some more exotic characters, you'll have to use some workaround.
One of the workarounds are Escape sequences. This way you can for example represent a new line in your string simply by adding two easily typable characters \n to your string literal. So when you print the 'hello\nworld' string, the words will be printed on separate lines. That's very handy!
On the other hand, sometimes you might want to include the actual characters \ and n into your string – you might not want them to be interpreted as a new line. Look at these examples:
'New updates are ready in c:\windows\updates\new'
'In this lesson we will learn what the \n escape sequence does.'
In such situations you can just prefix the string literal with the r character like this: r'hello\nworld' and no escape sequences will be interpreted by Python. The string will be printed exactly as you created it.
Raw string literals are not completely "raw"?
Many people expect the raw string literals to be raw in a sense that "anything placed between the quotes is ignored by Python". That is not true. Python still recognizes all the escape sequences, it just does not interpret them - it leaves them unchanged instead. It means that raw string literals still have to be valid string literals.
From the lexical definition of a string literal:
string ::= "'" stringitem* "'"
stringitem ::= stringchar | escapeseq
stringchar ::= <any source character except "\" or newline or the quote>
escapeseq ::= "\" <any source character>
It is clear that string literals (raw or not) containing a bare quote character: 'hello'world' or ending with a backslash: 'hello world\' are not valid.
Maybe this is obvious, maybe not, but you can make the string '\' by calling x=chr(92)
x=chr(92)
print type(x), len(x) # <type 'str'> 1
y='\\'
print type(y), len(y) # <type 'str'> 1
x==y # True
x is y # False
While asking this question, I realized I didn't know much about raw strings. For somebody claiming to be a Django trainer, this sucks.
I know what an encoding is, and I know what u'' alone does since I get what is Unicode.
But what does r'' do exactly? What kind of string does it result in?
And above all, what the heck does ur'' do?
Finally, is there any reliable way to go back from a Unicode string to a simple raw string?
Ah, and by the way, if your system and your text editor charset are set to UTF-8, does u'' actually do anything?
There's not really any "raw string"; there are raw string literals, which are exactly the string literals marked by an 'r' before the opening quote.
A "raw string literal" is a slightly different syntax for a string literal, in which a backslash, \, is taken as meaning "just a backslash" (except when it comes right before a quote that would otherwise terminate the literal) -- no "escape sequences" to represent newlines, tabs, backspaces, form-feeds, and so on. In normal string literals, each backslash must be doubled up to avoid being taken as the start of an escape sequence.
This syntax variant exists mostly because the syntax of regular expression patterns is heavy with backslashes (but never at the end, so the "except" clause above doesn't matter) and it looks a bit better when you avoid doubling up each of them -- that's all. It also gained some popularity to express native Windows file paths (with backslashes instead of regular slashes like on other platforms), but that's very rarely needed (since normal slashes mostly work fine on Windows too) and imperfect (due to the "except" clause above).
r'...' is a byte string (in Python 2.*), ur'...' is a Unicode string (again, in Python 2.*), and any of the other three kinds of quoting also produces exactly the same types of strings (so for example r'...', r'''...''', r"...", r"""...""" are all byte strings, and so on).
Not sure what you mean by "going back" - there is no intrinsically back and forward directions, because there's no raw string type, it's just an alternative syntax to express perfectly normal string objects, byte or unicode as they may be.
And yes, in Python 2.*, u'...' is of course always distinct from just '...' -- the former is a unicode string, the latter is a byte string. What encoding the literal might be expressed in is a completely orthogonal issue.
E.g., consider (Python 2.6):
>>> sys.getsizeof('ciao')
28
>>> sys.getsizeof(u'ciao')
34
The Unicode object of course takes more memory space (very small difference for a very short string, obviously ;-).
There are two types of string in Python 2: the traditional str type and the newer unicode type. If you type a string literal without the u in front you get the old str type which stores 8-bit characters, and with the u in front you get the newer unicode type that can store any Unicode character.
The r doesn't change the type at all, it just changes how the string literal is interpreted. Without the r, backslashes are treated as escape characters. With the r, backslashes are treated as literal. Either way, the type is the same.
ur is of course a Unicode string where backslashes are literal backslashes, not part of escape codes.
You can try to convert a Unicode string to an old string using the str() function, but if there are any unicode characters that cannot be represented in the old string, you will get an exception. You could replace them with question marks first if you wish, but of course this would cause those characters to be unreadable. It is not recommended to use the str type if you want to correctly handle unicode characters.
'raw string' means it is stored as it appears. For example, '\' is just a backslash instead of an escaping.
Let me explain it simply:
In python 2, you can store string in 2 different types.
The first one is ASCII which is str type in python, it uses 1 byte of memory. (256 characters, will store mostly English alphabets and simple symbols)
The 2nd type is UNICODE which is unicode type in python. Unicode stores all types of languages.
By default, python will prefer str type but if you want to store string in unicode type you can put u in front of the text like u'text' or you can do this by calling unicode('text')
So u is just a short way to call a function to cast str to unicode. That's it!
Now the r part, you put it in front of the text to tell the computer that the text is raw text, backslash should not be an escaping character. r'\n' will not create a new line character. It's just plain text containing 2 characters.
If you want to convert str to unicode and also put raw text in there, use ur because ru will raise an error.
NOW, the important part:
You cannot store one backslash by using r, it's the only exception.
So this code will produce error: r'\'
To store a backslash (only one) you need to use '\\'
If you want to store more than 1 characters you can still use r like r'\\' will produce 2 backslashes as you expected.
I don't know the reason why r doesn't work with one backslash storage but the reason isn't described by anyone yet. I hope that it is a bug.
A "u" prefix denotes the value has type unicode rather than str.
Raw string literals, with an "r" prefix, escape any escape sequences within them, so len(r"\n") is 2. Because they escape escape sequences, you cannot end a string literal with a single backslash: that's not a valid escape sequence (e.g. r"\").
"Raw" is not part of the type, it's merely one way to represent the value. For example, "\\n" and r"\n" are identical values, just like 32, 0x20, and 0b100000 are identical.
You can have unicode raw string literals:
>>> u = ur"\n"
>>> print type(u), len(u)
<type 'unicode'> 2
The source file encoding just determines how to interpret the source file, it doesn't affect expressions or types otherwise. However, it's recommended to avoid code where an encoding other than ASCII would change the meaning:
Files using ASCII (or UTF-8, for Python 3.0) should not have a coding cookie. Latin-1 (or UTF-8) should only be used when a comment or docstring needs to mention an author name that requires Latin-1; otherwise, using \x, \u or \U escapes is the preferred way to include non-ASCII data in string literals.
Unicode string literals
Unicode string literals (string literals prefixed by u) are no longer used in Python 3. They are still valid but just for compatibility purposes with Python 2.
Raw string literals
If you want to create a string literal consisting of only easily typable characters like english letters or numbers, you can simply type them: 'hello world'. But if you want to include also some more exotic characters, you'll have to use some workaround.
One of the workarounds are Escape sequences. This way you can for example represent a new line in your string simply by adding two easily typable characters \n to your string literal. So when you print the 'hello\nworld' string, the words will be printed on separate lines. That's very handy!
On the other hand, sometimes you might want to include the actual characters \ and n into your string – you might not want them to be interpreted as a new line. Look at these examples:
'New updates are ready in c:\windows\updates\new'
'In this lesson we will learn what the \n escape sequence does.'
In such situations you can just prefix the string literal with the r character like this: r'hello\nworld' and no escape sequences will be interpreted by Python. The string will be printed exactly as you created it.
Raw string literals are not completely "raw"?
Many people expect the raw string literals to be raw in a sense that "anything placed between the quotes is ignored by Python". That is not true. Python still recognizes all the escape sequences, it just does not interpret them - it leaves them unchanged instead. It means that raw string literals still have to be valid string literals.
From the lexical definition of a string literal:
string ::= "'" stringitem* "'"
stringitem ::= stringchar | escapeseq
stringchar ::= <any source character except "\" or newline or the quote>
escapeseq ::= "\" <any source character>
It is clear that string literals (raw or not) containing a bare quote character: 'hello'world' or ending with a backslash: 'hello world\' are not valid.
Maybe this is obvious, maybe not, but you can make the string '\' by calling x=chr(92)
x=chr(92)
print type(x), len(x) # <type 'str'> 1
y='\\'
print type(y), len(y) # <type 'str'> 1
x==y # True
x is y # False
I got the following code to handle Chinese character problem, or some special character in powerpoint file , because I would like to use the content of the ppt as the filename to save.
If it contains some special character, it will throw some exception, so I use the following code to handle it.
It works fine under Python 2.7 , but when I run with Python 3.0 it gives me the following error :
if not (char in '<>:"/\|?*'):
TypeError: 'in <string>' requires string as left operand, not int
I Googled the error message but I don't understand how to resolve it. I know the code if not (char in '<>:"/\|?*'): is to convert the character to ASCII code number, right?
Is there any example to fix my problem in Python 3?
def rm_invalid_char(self,str):
final=""
dosnames=['CON', 'PRN', 'AUX', 'NUL', 'COM1', 'COM2', 'COM3', 'COM4', 'COM5', 'COM6', 'COM7', 'COM8', 'COM9', 'LPT1', 'LPT2', 'LPT3', 'LPT4', 'LPT5', 'LPT6', 'LPT7', 'LPT8', 'LPT9']
for char in str:
if not (char in '<>:"/\|?*'):
if ord(char)>31:
final+=char
if final in dosnames:
#oh dear...
raise SystemError('final string is a DOS name!')
elif final.replace('.', '')=='':
print ('final string is all periods!')
pass
return final
Simple: use this
re.escape(YourStringHere)
From the docs:
Return string with all non-alphanumerics backslashed; this is useful
if you want to match an arbitrary literal string that may have regular
expression metacharacters in it.
You are passing an iterable whose first element is an integer (232) to rm_invalid_char(). The problem does not lie with this function, but with the caller.
Some debugging is in order: right at the beginning of rm_invalid_char(), you should do print(repr(str)): you will not see a string, contrary to what is expected by rm_invalid_char(). You must fix this until you see the string that you were expecting, by adjusting the code before rm_invalid_char() is called.
The problem is likely due to how Python 2 and Python 3 handle strings (in Python 2, str objects are strings of bytes, while in Python 3, they are strings of characters).
I'm curious why there is something in "str" that is acting like an integer - something strange is going on with the input.
However, I suspect if you:
Change the name of your str value to something else, e.g. char_string
Right after for char in char_string coerce whatever your input is to a string
then the problem you describe will be solved.
You might also consider adding a random bit to the end of your generated file name so you don't have to worry about colliding with the DOS reserved names.