Using isinstance() & issubclass() in Python
isinstance()
The builtin function isinstance(obj, cls) returns True if obj is an instance of class cls, else returns False.
>>> help(isinstance)
Help on built-in function isinstance in module builtins:
isinstance(...)
isinstance(object, class-or-type-or-tuple) -> bool
Return whether an object is an instance of a class or of a subclass thereof.
With a type as second argument, return whether that is the object's type.
The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
isinstance(x, A) or isinstance(x, B) or ... (etc.).
### EXAMPLES ###
>>> if isinstance(4, int):
print("4 is an integer!")
4 is an integer!
>>> isinstance(4, str)
False
>>> isinstance(4, int)
True
>>> class Man(object): pass
>>> ethan = Man()
>>> isinstance(ethan, Man)
True
If you are uncertain about the exact parent class of the object, you can insert all the likely classes in the form of a tuple. The isinstance() function will return True if the object belongs to either of the specified classes.
>>> isinstance(4, (str, int) ) True
Keep in mind that all builtin-classes, data types, user-defined classes inherit from the class called object.
issubclass()
The builtin function issubclass(subClass, superClass) returns True if the class subClass is a subclass of the class superClass, else it returns False.
>>> help(issubclass)
Help on built-in function issubclass in module builtins:
issubclass(...)
issubclass(C, B) -> bool
Return whether class C is a subclass (i.e., a derived class) of class B.
When using a tuple as the second argument issubclass(X, (A, B, ...)),
is a shortcut for issubclass(X, A) or issubclass(X, B) or ... (etc.).
### EXAMPLE ###
>>> class Person(object): pass
>>> class Man(Person): pass
>>> class Woman(Person): pass
>>> issubclass(Man, Person)
True
>>> issubclass(Man, object)
True
>>> issubclass(Woman, Man)
False
If you are uncertain about the exact parent class of a subclass, you can insert all the likely classes in the form of a tuple. The issubclass() function will return True if the class specified is a subclass of either of the specified classes.
>>> issubclass( Man, (Person, Woman) ) True >>> issubclass( Person, (Man, Woman) ) False
Keep in mind that all builtin-classes, data types, user-defined classes inherit from the class called object.
See also:
- Python 101
- Object Oriented Python
- Design Patterns in Python
- 50+ Handy Standard Library Modules
- 60+ Handy Third Library Modules
- 50+ Tips & Tricks for Python Developers
- 50+ Know-How(s) Every Pythonista Must Know