Any way to stringify a variable id / symbol in Python?

Question

I'm wondering if it is possible at all in python to stringify variable id/symbol -- that is, a function that behaves as follows:

>>> symbol = 'whatever'
>>> symbol_name(symbol)
'symbol'

Now, it is easy to do it on a function or a class (if it is a direct reference to the object):

>>> def fn(): pass
>>> fn.func_name
'fn'

But I'm looking for a general method that works on all cases, even for indirect object references. I've thought of somehow using id(var), but no luck yet.

Is there any way to do it?

possible duplicate of python, can i print original var name? — Anycorn
– Anycorn, Commented Jun 8, 2010 at 19:39
I'm looking at the actual source code of NameError in python26/Python/ceval.c as obviously NameError does get the symbol name right. (As I noted below, symbol_name(non_existent) yields a traceback with "NameError: name 'non_existent' is not defined" message.) PyTuple_GetItem (and PyDict_GetItem) yields the symbol name I want, but I haven't found an interface that wraps it and reveals it to the user. So unless someone proves me otherwise, it may well be impossible. For any instance variable of a class, it is possible by overriding getattribute and grepping NameError, however. — OTZ
– OTZ, Commented Jun 8, 2010 at 20:35

Tarantula · Accepted Answer · 2010-06-08 19:56:54Z

4

Here is, I'm sure you can turn it into a better form =)

def symbol_name(a):
    for k,v in globals().items():
        if id(a)==id(v): return k

Update: As unbeli has noted, if you have:

a = []
b = a

The function will not be able to show you the right name, since id(a)==id(b).

edited Jun 8, 2010 at 19:56

answered Jun 8, 2010 at 19:40

Tarantula

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6 Comments

unbeli Over a year ago

>>> symbol_name(a) 'a' >>> b=a >>> symbol_name(b) 'a' oops

Jim Dennis Over a year ago

Given that any object can have multiple names, wouldn't this be slightly better: if a is v: results.append(k) ... (assuming you wrap the loop in an instantiation and return of "results").

unbeli Over a year ago

still cannot tell the difference between two equal variables. Obviously, if id(x)==id(y), then symbol_name(x) == symbol_name(y), but should be 'x' != 'y'

Jim Dennis Over a year ago

Are you trying to provide debugging information? Might you consider using the traceback module? If you're trying to report "the name" of an object you might have to search through locals() and globals() and ... I'm not sure sure what other name spaces.

Tarantula Over a year ago

unbeli is right, it works not for all cases, if two variables have the same id, it may return the wrong name.

|

unbeli · Accepted Answer · 2010-06-08 19:35:28Z

3

I don't think it's possible. Even for functions, that is not the variable name:

>>> def fn(): pass
... 
>>> fn.func_name
'fn'
>>> b=fn
>>> b.func_name
'fn'
>>> del fn
>>> b.func_name
'fn'
>>> b()
>>> fn()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'fn' is not defined

answered Jun 8, 2010 at 19:35

unbeli

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Comments

OTZ · Accepted Answer · 2010-08-30 10:10:38Z

-1

"Not possible" is the answer.

answered Aug 30, 2010 at 10:10

OTZ

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1 Comment

NeilG Over a year ago

Might be partially possible answer here: stackoverflow.com/a/9121991/134044 which in turn refers to a "yes it is possible" answer (with caveats) here: stackoverflow.com/a/8875313/134044

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