How to check whether a variable is a class or not?

Question

I was wondering how to check whether a variable is a class (not an instance!) or not.

I\'ve tried to use the function isinstance(object, class_or_type_or_tuple

Answer 1

There are some working solutions here already, but here's another one:

>>> import types
>>> class Dummy: pass
>>> type(Dummy) is types.ClassType
True

Answer 2

This check is compatible with both Python 2.x and Python 3.x.

import six
isinstance(obj, six.class_types)

This is basically a wrapper function that performs the same check as in andrea_crotti answer.

Example:

>>> import datetime
>>> isinstance(datetime.date, six.class_types)
>>> True
>>> isinstance(datetime.date.min, six.class_types)
>>> False

Answer 3

The inspect.isclass is probably the best solution, and it's really easy to see how it's actually implemented

def isclass(object):
    """Return true if the object is a class.

    Class objects provide these attributes:
        __doc__         documentation string
        __module__      name of module in which this class was defined"""
    return isinstance(object, (type, types.ClassType))

Answer 4

simplest way is to use inspect.isclass as posted in the most-voted answer.
the implementation details could be found at python2 inspect and python3 inspect.
for new-style class: isinstance(object, type)
for old-style class: isinstance(object, types.ClassType)
em, for old-style class, it is using types.ClassType, here is the code from types.py:

class _C:
    def _m(self): pass
ClassType = type(_C)

Answer 5

Even better: use the inspect.isclass function.

>>> import inspect
>>> class X(object):
...     pass
... 
>>> inspect.isclass(X)
True

>>> x = X()
>>> isinstance(x, X)
True
>>> y = 25
>>> isinstance(y, X)
False

Answer 6

class Foo: is called old style class and class X(object): is called new style class.

Check this What is the difference between old style and new style classes in Python? . New style is recommended. Read about "unifying types and classes"