Can you get the instance variable name from a class?

Question

I understand that you should never use variable names within the program, but I am using is strictly for debug purposes and would like to convey the name of the variable to the user for readability.

I have a file like this:

class MyClass(object):
    def __init__(self):
        pass

    def foo(msg=""):
        debug("Called from the %s instance.") #quazi-print function that only prints when a DEBUG variable is True.
        print(msg)

m = MyClass()
m.foo("Test")

I would like to retrieve the m instance variable name from within the class itself. Though this is merely an example file, I am using it to convey to the user that a raw socket has been created at a certain attribute within an instance variable, and would like to show where it is (i.e. New socket at m.socket)

Is this feasible with Python?

Solution 1

You could look in the instance's globals dictionary and find the item that has its self as a value.

class Foo(object):
    def bar(self):
        return [k for k,v in globals().items() if v is self]
    def bah(self):
        d = {v:k for k,v in globals().items()}
        return d[self]

f = Foo()
g = Foo()

print f.bar(), g.bar()
print f.bah(), g.bah()

>>> 
['f'] ['g']
f g
>>> 

Solution 2

Here's a really silly way to do it, if you don't mind the program exiting at that point: add this line to foo():

print undefined_variable

And when you get there, you get a stack trace like this:

Traceback (most recent call last): File "test.py", line 15, in <module> m.foo("Test") File "test.py", line 11, in foo print undefined_variable NameError: global name 'undefined_variable' is not defined

...which tells you that the name of the variable that called it was 'm' :)

(You might be able to do something like this using the traceback module, without killing the program. I've tried a few ways, but haven't managed to get it to include the m.foo() line in the output.)