python – Getting the name of a variable as a string

python – Getting the name of a variable as a string

With Python 3.8 one can simply use f-string debugging feature:

>>> foo = dict()
>>> f{foo=}.split(=)[0]
foo 

One drawback of this method is that in order to get foo printed you have to add f{foo=} yourself. In other words, you already have to know the name of the variable. In other words, the above code snippet is exactly the same as just

>>> foo

Please see the other answers here that might be applicable to answer the question.

The only objects in Python that have canonical names are modules, functions, and classes, and of course there is no guarantee that this canonical name has any meaning in any namespace after the function or class has been defined or the module imported. These names can also be modified after the objects are created so they may not always be particularly trustworthy.

What you want to do is not possible without recursively walking the tree of named objects; a name is a one-way reference to an object. A common or garden-variety Python object contains no references to its names. Imagine if every integer, every dict, every list, every Boolean needed to maintain a list of strings that represented names that referred to it! It would be an implementation nightmare, with little benefit to the programmer.

python – Getting the name of a variable as a string

Even if variable values dont point back to the name, you have access to the list of every assigned variable and its value, so Im astounded that only one person suggested looping through there to look for your var name.

Someone mentioned on that answer that you might have to walk the stack and check everyones locals and globals to find foo, but if foo is assigned in the scope where youre calling this retrieve_name function, you can use inspects current frame to get you all of those local variables.

My explanation might be a little bit too wordy (maybe I shouldve used a foo less words), but heres how it would look in code (Note that if there is more than one variable assigned to the same value, you will get both of those variable names):

import inspect

x, y, z = 1, 2, 3

def retrieve_name(var):
    callers_local_vars = inspect.currentframe().f_back.f_locals.items()
    return [var_name for var_name, var_val in callers_local_vars if var_val is var]

print(retrieve_name(y))

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If youre calling this function from another function, something like:

def foo(bar):
    return retrieve_name(bar)

foo(baz)

And you want the baz instead of bar, youll just need to go back a scope further. This can be done by adding an extra .f_back in the caller_local_vars initialization.

See an example here: ideone