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

>>> class X(object):
...     pass
... 
>>> type(X)
<type 'type'>
>>> isinstance(X,type)
True

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“

isinstance(X, type)

Return True if X is class and False if not.

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

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

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

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

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

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)

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

Benjamin Peterson is correct about the use of inspect.isclass() for this job.
But note that you can test if a Class object is a specific Class, and therefore implicitly a Class, using the built-in function issubclass.
Depending on your use-case this can be more pythonic.

from typing import Type, Any
def isclass(cl: Type[Any]):
    try:
        return issubclass(cl, cl)
    except TypeError:
        return False

Can then be used like this:

>>> class X():
...     pass
... 
>>> isclass(X)
True
>>> isclass(X())
False

There is an alternative way to check it:

import inspect

class cls():
     print(None)

inspect.isclass(cls)

Reference: https://www.kite.com/python/docs/inspect.isclass

Well, inspect.isclass is not working for me, instead, try this

class foo:
    pass

var = foo()

if str(type(var)).split(".")[0] == "<class '__main__":
    print("this is a class")
else:
    print(str(type(var)).split(".")[0])

So basically, type(var) is <class 'a type'>

Example: <class 'int'
But, when var is a class, it will appear something like <class '__main__.classname'>

So we split the string into <class '__main__ and we compare using if, if the string fit perfectly then it’s a class

In some cases (depending on your system), a simple test is to see if your variable has a __module__ attribute.

if getattr(my_variable,'__module__', None):
    print(my_variable, ".__module__ is ",my_variable.__module__)
else:
    print(my_variable,' has no __module__.')

int, float, dict, list, str etc do not have __module__

If you are using a class decorator, inspect.isclass() will not work since the class is wrapped by a function. Instead, use inspect.unwrap() first, then test with inspect.isclass().

Example:

import functools
import inspect

def class_decorator(cls):
    @functools.wraps(cls)
    def wrapper(*args, **kwargs):
        return cls(*args, **kwargs)
    return wrapper

@class_decorator
class Spam:
    pass

print(inspect.isclass(Spam)) # False
print(type(Spam)) # class 'function'

print(inspect.isclass(inspect.unwrap(Spam))) # True
print(inspect.unwrap(Spam)) # class 'Spam'