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Getting name of local variable at runtime in Python3

I want to get variable name in function so here:
def foo(bar):
print(getLocalVaribalename(bar))
I want 'bar' to be printed.
so I found the code for global variables
def varName(variable,globalOrLocal=globals()):
for name in list(globalOrLocal.keys()):
expression = f'id({name})'
if id(variable) == eval(expression):
return name
and I sent varName(bar,locals()) to it like this
def foo(bar):
print(varName(bar,locals()))
but gives NameError: name 'bar' is not defined error.
I also found Getting name of local variable at runtime in Python which is for python 2 but the syntax is completely different. note that the main goal is to get the name of local variable and not necessarily with this code(varName function which is defined few lines earlier).

import sys
def getlocalnamesforobj(obj):
frame = sys._getframe(1)
return [key for key, value in frame.f_locals.items() if value is obj]
This introspects the local variables from the calling function.
One obvious problem is, of course, there might be more than one name pointing to the same object, so the function returns a list of names.
As put in the comments, however, I can't perceive how this can be of any use in any real code.
As a rule of thumb, if you need variable names as data (strings), you probably should be using a dictionary to store your data instead.

How can I pass on called function value in Python?

Let's say I have a code like this:
def read_from_file(filename):
list = []
for i in filename:
value = i[0]
list.append(value)
return list
def other_function(other_filename):
"""
That's where my question comes in. How can I get the list
from the other function if I do not know the value "filename" will get?
I would like to use the "list" in this function
"""
read_from_file("apples.txt")
other_function("pears.txt")
I'm aware that this code might not work or might not be perfect. But the only thing I need is the answer to my question in the code.

You have two general options. You can make your list a global variable that all functions can access (usually this is not the right way), or you can pass it to other_function (the right way). So
def other_function(other_filename, anylist):
pass # your code here
somelist = read_from_file("apples.txt")
other_function("pears.txt.", somelist)

You need to "catch" the value return from the first function, and then pass that to the second function.
file_name = read_from_file('apples.txt')
other_function(file_name)

You need to store the returned value in a variable before you can pass it onto another function.
a = read_from_file("apples.txt")

There are at least three reasonable ways to achieve this and two which a beginner will probably never need:
Store the returned value of read_from_file and give it as a parameter to other_function (so adjust the signature to other_function(other_filename, whatever_list))
Make whatever_list a global variable.
Use an object and store whatever_list as a property of that object
(Use nested functions)
(Search for the value via garbage collector gc ;-)
)
Nested functions
def foo():
bla = "OK..."
def bar():
print(bla)
bar()
foo()
Global variables
What are the rules for local and global variables in Python? (official docs)
Global and Local Variables
Very short example
Misc
You should not use list as a variable name as you're overriding a built-in function.
You should use a descriptive name for your variables. What is the content of the list?
Using global variables can sometimes be avoided in a good way by creating objects. While I'm not always a fan of OOP, it sometimes is just what you need. Just have a look of one of the plenty tutorials (e.g. here), get familiar with it, figure out if it fits for your task. (And don't use it all the time just because you can. Python is not Java.)

python static variables and methods

I know there have been several posts about this, but I am still confused. Am trying to use a static variable with initialization, and don't know how to do it. So what I have is a package 'config', which has a module the_config.py. What I would like is for this to be something like
# the_config.py
import yaml
user_settings=None
def initialize(user_settings_file)
with open(user_settings_file) as yaml_handle:
user_settings = yaml.safe_load(user_settings_file)
Then there would be a calling module as pipeline.py
#pipeline.py
import config.the_config as my_config
def main(argv):
...
my_config.intialize(user_settings_file)
print my_config.user_settings['Output_Dir']
But this doesn't work. How should I be doing this please?
Thanks in advance.

When you assign to user_settings, it is automatically treated as a local variable in the initialize function. To tell Python that the assignment is intended to change the global variable instead, you need to write
global user_settings
at the beginning of initialize.

In Python any variable that is assigned in the body of a function is considered a local variable, unless it's has been explicitly declared differently with either global or nonlocal declarations.
Python considers also assignment any "augmented-assignment" operator like += or /=.
The mandatory declaration of global that are modified is a (little) price to pay to the fact that in Python there is no need to declare variables.
It's also assumed that your code doesn't rely too much on mutating state in that is kept global variables so if your code requires a lot of global declarations then there's probably something wrong.

I can propose You some way to solve this.
First of all the root of your problem is creation of new local variable in your initialize function
user_settings = yaml.safe_load(user_settings_file)
As soon as there is equal sign right to variable name python create new variable in corresponding scope (in this case local for initialize function
to avoid this one can use following:
use global declaration
def initialize(user_settings_file)
global user_settings # here it is
with open(user_settings_file) as yaml_handle:
user_settings = yaml.safe_load(user_settings_file)
modify existing variable but not create new one
user_settings = {}
def initialize(user_settings_file)
with open(user_settings_file) as yaml_handle:
user_settings.update(yaml.safe_load(user_settings_file)) # here we modify existing user_settings
operate with module attribute (this one is quite tricky)
user_settings = {}
def initialize(user_settings_file)
with open(user_settings_file) as yaml_handle:
import the_config
the_config.user_settings = yaml.safe_load(user_settings_file)

add a local variables to a function

is it possible to add a local varible to a function, just before calling it ? if yes how ?
EDIT:REASON
i noticed that all my views in django are using
render_to_response(template_name,locals())
now i created a middleware and i wanted to add one more local variable using the
def process_view():
method of it .so that i don't have to modify the views .

The local scope for a function does not exist until the function is called, so it's not possible to do this. You could do this for a closure, but the next person to have to maintain the code would hunt you down and kill you.

Although I also think it is pretty useless, I thought that you may enclose the function in either a 'with' statement or another function, like the code below. Of course, this approach can be accomplished directly within the function of interest. In fact, you are adding the local variable 'during' the function declaration. See if this fits your needs!
#!/usr/bin/python
def my_funct(_local):
"""My function of interest
"""
print "Local argument was %s" % str(_local)
return "Finished"
def localize(fct, local_var):
"""
"""
return fct(_local = local_var)
## Use function to 'localize' variable
localize(my_funct, local_var="LOCAL_VARIABLE")
## Same effect without supplementary function :
my_funct(_local="LOCAL_VARIABLE")
try:
print local_var
except:
print "No such global variable"
Just some thoughts :)
Cheers

So if you’re one of those lazy
programmers and you like keeping code
particularly concise, you can take
advantage of a built-in Python
function called locals(). It returns a
dictionary mapping all local variable
names to their values, where “local”
means all variables that have been
defined within the current scope.
source
It is a trick in order to not have to explicitly list all of the variables you need to pass in to the function. In this case, you need to explicitly state a variable to pass in. Therefore, you should not be using locals() in the calls you are making in your middle-ware, as the trick was not designed to be used like that.

i mangaged to do that using decorators.

How to create module-wide variables in Python? [duplicate]

This question already has answers here:
Using global variables in a function
(25 answers)
Closed 3 years ago.
The community reviewed whether to reopen this question 4 months ago and left it closed:
Original close reason(s) were not resolved
Is there a way to set up a global variable inside of a module? When I tried to do it the most obvious way as appears below, the Python interpreter said the variable __DBNAME__ did not exist.
...
__DBNAME__ = None
def initDB(name):
if not __DBNAME__:
__DBNAME__ = name
else:
raise RuntimeError("Database name has already been set.")
...
And after importing the module in a different file
...
import mymodule
mymodule.initDB('mydb.sqlite')
...
And the traceback was:
...
UnboundLocalError: local variable 'DBNAME' referenced before assignment
...
Any ideas? I'm trying to set up a singleton by using a module, as per this fellow's recommendation.

Here is what is going on.
First, the only global variables Python really has are module-scoped variables. You cannot make a variable that is truly global; all you can do is make a variable in a particular scope. (If you make a variable inside the Python interpreter, and then import other modules, your variable is in the outermost scope and thus global within your Python session.)
All you have to do to make a module-global variable is just assign to a name.
Imagine a file called foo.py, containing this single line:
X = 1
Now imagine you import it.
import foo
print(foo.X) # prints 1
However, let's suppose you want to use one of your module-scope variables as a global inside a function, as in your example. Python's default is to assume that function variables are local. You simply add a global declaration in your function, before you try to use the global.
def initDB(name):
global __DBNAME__ # add this line!
if __DBNAME__ is None: # see notes below; explicit test for None
__DBNAME__ = name
else:
raise RuntimeError("Database name has already been set.")
By the way, for this example, the simple if not __DBNAME__ test is adequate, because any string value other than an empty string will evaluate true, so any actual database name will evaluate true. But for variables that might contain a number value that might be 0, you can't just say if not variablename; in that case, you should explicitly test for None using the is operator. I modified the example to add an explicit None test. The explicit test for None is never wrong, so I default to using it.
Finally, as others have noted on this page, two leading underscores signals to Python that you want the variable to be "private" to the module. If you ever do an import * from mymodule, Python will not import names with two leading underscores into your name space. But if you just do a simple import mymodule and then say dir(mymodule) you will see the "private" variables in the list, and if you explicitly refer to mymodule.__DBNAME__ Python won't care, it will just let you refer to it. The double leading underscores are a major clue to users of your module that you don't want them rebinding that name to some value of their own.
It is considered best practice in Python not to do import *, but to minimize the coupling and maximize explicitness by either using mymodule.something or by explicitly doing an import like from mymodule import something.
EDIT: If, for some reason, you need to do something like this in a very old version of Python that doesn't have the global keyword, there is an easy workaround. Instead of setting a module global variable directly, use a mutable type at the module global level, and store your values inside it.
In your functions, the global variable name will be read-only; you won't be able to rebind the actual global variable name. (If you assign to that variable name inside your function it will only affect the local variable name inside the function.) But you can use that local variable name to access the actual global object, and store data inside it.
You can use a list but your code will be ugly:
__DBNAME__ = [None] # use length-1 list as a mutable
# later, in code:
if __DBNAME__[0] is None:
__DBNAME__[0] = name
A dict is better. But the most convenient is a class instance, and you can just use a trivial class:
class Box:
pass
__m = Box() # m will contain all module-level values
__m.dbname = None # database name global in module
# later, in code:
if __m.dbname is None:
__m.dbname = name
(You don't really need to capitalize the database name variable.)
I like the syntactic sugar of just using __m.dbname rather than __m["DBNAME"]; it seems the most convenient solution in my opinion. But the dict solution works fine also.
With a dict you can use any hashable value as a key, but when you are happy with names that are valid identifiers, you can use a trivial class like Box in the above.

Explicit access to module level variables by accessing them explicity on the module
In short: The technique described here is the same as in steveha's answer, except, that no artificial helper object is created to explicitly scope variables. Instead the module object itself is given a variable pointer, and therefore provides explicit scoping upon access from everywhere. (like assignments in local function scope).
Think of it like self for the current module instead of the current instance !
# db.py
import sys
# this is a pointer to the module object instance itself.
this = sys.modules[__name__]
# we can explicitly make assignments on it
this.db_name = None
def initialize_db(name):
if (this.db_name is None):
# also in local function scope. no scope specifier like global is needed
this.db_name = name
# also the name remains free for local use
db_name = "Locally scoped db_name variable. Doesn't do anything here."
else:
msg = "Database is already initialized to {0}."
raise RuntimeError(msg.format(this.db_name))
As modules are cached and therefore import only once, you can import db.py as often on as many clients as you want, manipulating the same, universal state:
# client_a.py
import db
db.initialize_db('mongo')
# client_b.py
import db
if (db.db_name == 'mongo'):
db.db_name = None # this is the preferred way of usage, as it updates the value for all clients, because they access the same reference from the same module object
# client_c.py
from db import db_name
# be careful when importing like this, as a new reference "db_name" will
# be created in the module namespace of client_c, which points to the value
# that "db.db_name" has at import time of "client_c".
if (db_name == 'mongo'): # checking is fine if "db.db_name" doesn't change
db_name = None # be careful, because this only assigns the reference client_c.db_name to a new value, but leaves db.db_name pointing to its current value.
As an additional bonus I find it quite pythonic overall as it nicely fits Pythons policy of Explicit is better than implicit.

Steveha's answer was helpful to me, but omits an important point (one that I think wisty was getting at). The global keyword is not necessary if you only access but do not assign the variable in the function.
If you assign the variable without the global keyword then Python creates a new local var -- the module variable's value will now be hidden inside the function. Use the global keyword to assign the module var inside a function.
Pylint 1.3.1 under Python 2.7 enforces NOT using global if you don't assign the var.
module_var = '/dev/hello'
def readonly_access():
connect(module_var)
def readwrite_access():
global module_var
module_var = '/dev/hello2'
connect(module_var)

For this, you need to declare the variable as global. However, a global variable is also accessible from outside the module by using module_name.var_name. Add this as the first line of your module:
global __DBNAME__

You are falling for a subtle quirk. You cannot re-assign module-level variables inside a python function. I think this is there to stop people re-assigning stuff inside a function by accident.
You can access the module namespace, you just shouldn't try to re-assign. If your function assigns something, it automatically becomes a function variable - and python won't look in the module namespace.
You can do:
__DB_NAME__ = None
def func():
if __DB_NAME__:
connect(__DB_NAME__)
else:
connect(Default_value)
but you cannot re-assign __DB_NAME__ inside a function.
One workaround:
__DB_NAME__ = [None]
def func():
if __DB_NAME__[0]:
connect(__DB_NAME__[0])
else:
__DB_NAME__[0] = Default_value
Note, I'm not re-assigning __DB_NAME__, I'm just modifying its contents.