Class private method
__private_method starts with two underscores, declaring that the method is a private method and cannot be called outside the class.
Call slef.__private_methods inside the class.
Proprietary methods of class:
__init__ constructor, call
__del__ destructor when generating an object, use
__repr__ to print and convert
__setitem__ to assign according to index
__getitem__ to obtain according to index Value
__len__ gets length
__cmp__ comparison operation
__call__ function call
__add__ addition operation
__sub__ subtraction operation
__mul__ multiplication operation
__div__ division operation
__mod__ remainder operation
__pow__ weighing square