Convert Variable Name to String?

Question

I would like to convert a python variable name into the string equivalent as shown. Any ideas how?

var = {}
print ???  # Would like to see \'var\'
something_         


        

Answer 1

TL;DR: Not possible. See 'conclusion' at the end.

---

There is an usage scenario where you might need this. I'm not implying there are not better ways or achieving the same functionality.

This would be useful in order to 'dump' an arbitrary list of dictionaries in case of error, in debug modes and other similar situations.

What would be needed, is the reverse of the eval() function:

get_indentifier_name_missing_function()

which would take an identifier name ('variable','dictionary',etc) as an argument, and return a string containing the identifier’s name.

---

Consider the following current state of affairs:

random_function(argument_data)

If one is passing an identifier name ('function','variable','dictionary',etc) argument_data to a random_function() (another identifier name), one actually passes an identifier (e.g.: <argument_data object at 0xb1ce10>) to another identifier (e.g.: <function random_function at 0xafff78>):

<function random_function at 0xafff78>(<argument_data object at 0xb1ce10>)

From my understanding, only the memory address is passed to the function:

<function at 0xafff78>(<object at 0xb1ce10>)

Therefore, one would need to pass a string as an argument to random_function() in order for that function to have the argument's identifier name:

random_function('argument_data')

Inside the random_function()

def random_function(first_argument):

, one would use the already supplied string 'argument_data' to:

1. serve as an 'identifier name' (to display, log, string split/concat, whatever)

2. feed the eval() function in order to get a reference to the actual identifier, and therefore, a reference to the real data:

   print("Currently working on", first_argument)
   some_internal_var = eval(first_argument)
   print("here comes the data: " + str(some_internal_var))
   

Unfortunately, this doesn't work in all cases. It only works if the random_function() can resolve the 'argument_data' string to an actual identifier. I.e. If argument_data identifier name is available in the random_function()'s namespace.

This isn't always the case:

# main1.py
import some_module1

argument_data = 'my data'

some_module1.random_function('argument_data')


# some_module1.py
def random_function(first_argument):
    print("Currently working on", first_argument)
    some_internal_var = eval(first_argument)
    print("here comes the data: " + str(some_internal_var))
######

Expected results would be:

Currently working on: argument_data
here comes the data: my data

Because argument_data identifier name is not available in the random_function()'s namespace, this would yield instead:

Currently working on argument_data
Traceback (most recent call last):
  File "~/main1.py", line 6, in <module>
    some_module1.random_function('argument_data')
  File "~/some_module1.py", line 4, in random_function
    some_internal_var = eval(first_argument)
  File "<string>", line 1, in <module>
NameError: name 'argument_data' is not defined

---

Now, consider the hypotetical usage of a get_indentifier_name_missing_function() which would behave as described above.

Here's a dummy Python 3.0 code: .

# main2.py
import some_module2
some_dictionary_1       = { 'definition_1':'text_1',
                            'definition_2':'text_2',
                            'etc':'etc.' }
some_other_dictionary_2 = { 'key_3':'value_3',
                            'key_4':'value_4', 
                            'etc':'etc.' }
#
# more such stuff
#
some_other_dictionary_n = { 'random_n':'random_n',
                            'etc':'etc.' }

for each_one_of_my_dictionaries in ( some_dictionary_1,
                                     some_other_dictionary_2,
                                     ...,
                                     some_other_dictionary_n ):
    some_module2.some_function(each_one_of_my_dictionaries)


# some_module2.py
def some_function(a_dictionary_object):
    for _key, _value in a_dictionary_object.items():
        print( get_indentifier_name_missing_function(a_dictionary_object)    +
               "    " +
               str(_key) +
               "  =  " +
               str(_value) )
######

Expected results would be:

some_dictionary_1    definition_1  =  text_1
some_dictionary_1    definition_2  =  text_2
some_dictionary_1    etc  =  etc.
some_other_dictionary_2    key_3  =  value_3
some_other_dictionary_2    key_4  =  value_4
some_other_dictionary_2    etc  =  etc.
......
......
......
some_other_dictionary_n    random_n  =  random_n
some_other_dictionary_n    etc  =  etc.

Unfortunately, get_indentifier_name_missing_function() would not see the 'original' identifier names (some_dictionary_,some_other_dictionary_2,some_other_dictionary_n). It would only see the a_dictionary_object identifier name.

Therefore the real result would rather be:

a_dictionary_object    definition_1  =  text_1
a_dictionary_object    definition_2  =  text_2
a_dictionary_object    etc  =  etc.
a_dictionary_object    key_3  =  value_3
a_dictionary_object    key_4  =  value_4
a_dictionary_object    etc  =  etc.
......
......
......
a_dictionary_object    random_n  =  random_n
a_dictionary_object    etc  =  etc.

So, the reverse of the eval() function won't be that useful in this case.

---

Currently, one would need to do this:

# main2.py same as above, except:

    for each_one_of_my_dictionaries_names in ( 'some_dictionary_1',
                                               'some_other_dictionary_2',
                                               '...',
                                               'some_other_dictionary_n' ):
        some_module2.some_function( { each_one_of_my_dictionaries_names :
                                     eval(each_one_of_my_dictionaries_names) } )
    
    
    # some_module2.py
    def some_function(a_dictionary_name_object_container):
        for _dictionary_name, _dictionary_object in a_dictionary_name_object_container.items():
            for _key, _value in _dictionary_object.items():
                print( str(_dictionary_name) +
                       "    " +
                       str(_key) +
                       "  =  " +
                       str(_value) )
    ######

---

In conclusion:

• Python passes only memory addresses as arguments to functions.
• Strings representing the name of an identifier, can only be referenced back to the actual identifier by the eval() function if the name identifier is available in the current namespace.
• A hypothetical reverse of the eval() function, would not be useful in cases where the identifier name is not 'seen' directly by the calling code. E.g. inside any called function.
• Currently one needs to pass to a function:
  1. the string representing the identifier name
  2. the actual identifier (memory address)

This can be achieved by passing both the 'string' and eval('string') to the called function at the same time. I think this is the most 'general' way of solving this egg-chicken problem across arbitrary functions, modules, namespaces, without using corner-case solutions. The only downside is the use of the eval() function which may easily lead to unsecured code. Care must be taken to not feed the eval() function with just about anything, especially unfiltered external-input data.

Answer 2

Technically the information is available to you, but as others have asked, how would you make use of it in a sensible way?

>>> x = 52
>>> globals()
{'__builtins__': <module '__builtin__' (built-in)>, '__name__': '__main__', 
'x': 52, '__doc__': None, '__package__': None}

This shows that the variable name is present as a string in the globals() dictionary.

>>> globals().keys()[2]
'x'

In this case it happens to be the third key, but there's no reliable way to know where a given variable name will end up

>>> for k in globals().keys():
...   if not k.startswith("_"):
...     print k
...
x
>>>

You could filter out system variables like this, but you're still going to get all of your own items. Just running that code above created another variable "k" that changed the position of "x" in the dict.

But maybe this is a useful start for you. If you tell us what you want this capability for, more helpful information could possibly be given.

Answer 3

This will work for simnple data types (str, int, float, list etc.)

>>> def my_print(var_str) : 
      print var_str+':', globals()[var_str]
>>> a = 5
>>> b = ['hello', ',world!']
>>> my_print('a')
a: 5
>>> my_print('b')
b: ['hello', ',world!']

Answer 4

To get the variable name of var as a string:

var = 1000
var_name = [k for k,v in locals().items() if v == var][0] 
print(var_name) # ---> outputs 'var'

Answer 5

print "var"
print "something_else"

Or did you mean something_else?

Answer 6

as long as it's a variable and not a second class, this here works for me:

def print_var_name(variable):
 for name in globals():
     if eval(name) == variable:
        print name
foo = 123
print_var_name(foo)
>>>foo

this happens for class members:

class xyz:
     def __init__(self):
         pass
member = xyz()
print_var_name(member)
>>>member

ans this for classes (as example):

abc = xyz
print_var_name(abc)
>>>abc
>>>xyz

So for classes it gives you the name AND the properteries