querying class attributes when given the "name" of a class

Question

I have a case where the "names" of classes of interest are available.

Is it possible, without creating an instance of the class, to check for the existing and value of Class attributes ?

E.g., I know that one can do this

class Universal:
    answer = 42

all_knowing_one_class = Universal
solution = 'answer'
unknown = 'a great mystery'
print('The universal answer is', getattr(all_knowing_one_class, solution, unknown) )

But not clear how to do this if one starts with the string name of the class

class Universal:
    answer = 42

all_knowing_one_class_name = 'Universal'
solution = 'answer'
unknown = 'a great mystery'
print('The universal answer is', ??? )

I know that I could create a local mapping between name and class, but wondered if there was a more pythonic way that I could learn 🙂

Asked By: user20296510

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Source

Answer 1

You don’t need to create a local mapping between name and class, because such a mapping already exists – locals(). The dynamic namespace lookup can be done with either getitem or getattr style access: it’s getattr if you have the module instance itself, and getitem if you have the namespace (i.e. the module’s __dict__).

If you’re working within the same namespace:

the_class = locals()[all_knowing_one_class_name]

# or...

import __main__
the_class = getattr(__main__, all_knowing_one_class_name)

If the Universal class is defined in a different namespace, other_module.py say:

import other_module

the_class = vars(other_module)[all_knowing_one_class_name] 

# or

the_class = getattr(other_module, all_knowing_one_class_name)

If the name of "other_module.py" is also dynamic:

import importlib
other_module = importlib.import_module("other_module")

Answered By: wim

querying class attributes when given the "name" of a class

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