Proper way to assert type of variable in Python

Question

In using a function, I wish to ensure that the type of the variables are as expected. How to do it right?

Here is an example fake function trying to do just this before

Answer 1

Doing type('') is effectively equivalent to str and types.StringType

so type('') == str == types.StringType will evaluate to "True"

Note that Unicode strings which only contain ASCII will fail if checking types in this way, so you may want to do something like assert type(s) in (str, unicode) or assert isinstance(obj, basestring), the latter of which was suggested in the comments by 007Brendan and is probably preferred.

isinstance() is useful if you want to ask whether an object is an instance of a class, e.g:

class MyClass: pass

print isinstance(MyClass(), MyClass) # -> True
print isinstance(MyClass, MyClass()) # -> TypeError exception

But for basic types, e.g. str, unicode, int, float, long etc asking type(var) == TYPE will work OK.