isinstance(object,type) in python

type must be an object denoting a type/class, such as int or str. E.g., isinstance(1, int) evaluates to True, while isinstance(sys.stdin, str) evaluates to False. If you've defined a class Foo, then Foo is also a type object.

Edit: as @delnan notes, type itself is also a type in Python, so isinstance(str, type) is true because str is a type, while isinstance('foo', type) is false. object is also a type in Python, and is the root of the type hierarchy.

isinstance(object, classinfo)
object - object to be checked
classinfo - class, type, or tuple of classes and types

The isinstance() returns:
True if the object is an instance or subclass of a class, or any element of the tuple
False otherwise
eg: a = 1 + 2j

print(isinstance(1+2j, complex))
output : True

This statement checks if object has the type of type. The type variable should be a class.

isinstance(object, classinfo)

Return true if the object argument is an instance of the classinfo argument, or of a (direct, indirect or virtual) subclass thereof. Also return true if classinfo is a type object (new-style class) and object is an object of that type or of a (direct, indirect or virtual) subclass thereof. If object is not a class instance or an object of the given type, the function always returns false. If classinfo is neither a class object nor a type object, it may be a tuple of class or type objects, or may recursively contain other such tuples (other sequence types are not accepted). If classinfo is not a class, type, or tuple of classes, types, and such tuples, a TypeError exception is raised.

Changed in version 2.2: Support for a tuple of type information was added.

Quoted from: http://docs.python.org/library/functions.html#isinstance