Detailed introduction to Python's built-in isinstance function

English documentation:

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. If object is not an object of the given type, the function always returns false. If classinfo is a tuple of type objects (or recursively, other such tuples), return true if object is an instance of any of the types. If classinfo is not a type or tuple of types and such tuples, a TypeError exception is raised.

Description:

1. FunctionThe function is used to determine whether the object is an instance of a type object. The object parameter indicates the object that needs to be checked, and the calssinfo parameter indicates the type object.

　2. If the object parameter is an instance of a classinfo type object (or a direct, indirect, or virtual subclass of a classinfo class object), return True.

>>> isinstance(1,int)
True
>>> isinstance(1,str)
False

# 定义3各类：C继承B，B继承A
>>> class A:
    pass

>>> class B(A):
    pass

>>> class C(B):
    pass

>>> a = A()
>>> b = B()
>>> c = C()
>>> isinstance(a,A) #直接实例
True
>>> isinstance(a,B)
False
>>> isinstance(b,A) #子类实例 
True
>>> isinstance(c,A) #孙子类实例
True

　3. If the object parameter is passed in a type object, False will always be returned.

>>> isinstance(str,str)
False 
>>> isinstance(bool,int)
False

　4. If the classinfo type object is a tuple composed of multiple type objects, and if object object is an instance of any type object in the tuple, return True, otherwise return False.

>>> isinstance(a,(B,C))
False
>>> isinstance(a,(A,B,C))
True

　5. If the classinfo type object is not a type object or a tuple composed of multiple type objects, an error (TypeError) will be reported.

>>> isinstance(a,[A,B,C])
Traceback (most recent call last):
  File "<pyshell#23>", line 1, in <module>
    isinstance(a,[A,B,C])
TypeError: isinstance() arg 2 must be a type or tuple of types

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