Python Special Methods-Special method

Special methods

Special methods exist to be called to the Python interpreter, and usually do not need to call them directly.
This means that my_object.__len__ () should not be used, but should be called with Len (My_object).
When executing len (my_object), if My_object is an object of a custom class, the Python interpreter
To invoke the __len__ method of the owning class.

However, if My_object is a Python built-in type, such as List, str, ByteArray, ETC.,
Then the Python interpreter CPython will take a shortcut, and the __len__ method will actually return the Ob_size attribute directly in Pyvarobject.
Pyvarobject is a C-language struct that represents a variable-length built-in object in memory. Reading this value directly is much faster than calling a method.
Usually the invocation of a special method is implicit, such as for I in X: This statement is actually called the ITER (x) function,
And behind this function is the x.__iter__ () method. The premise, of course, is that this method is implemented in X.

Usually the code does not need to use special methods directly. An exception is the __init__ method, which requires that the constructor of the superclass (__init__) be called in the __init__ method of the subclass in the code.
For example, super (Basecls, self). __init__ (args).

Using special methods with built-in functions (such as Len, ITER, str, and so on) is the best choice. These built-in functions not only invoke special methods, they are usually faster.

List of special methods

Category	Method name
string/byte sequence representation	__repr__, __str__, __format__, __bytes__
numeric conversions	__abs__, __bool__, __complex__, __int__, __float__, __hash__, __index__
Set simulation	__len__, __getitem__, __setitem__, __delitem__, __contains__
Iterative enumeration	__iter__, __reversed__, __next__
Can call	__call__
Context Management	__ENTER__, __exit__
Creating and destroying instances	__new__, __init__, __del__
Property Management	__getattr__, __getattribute__, __setattr__, __delattr__, __dir__
Property descriptor	__get__, __set__, __delete__
Services related to the class	__prepare__, __instancecheck__, __subclasscheck__
Unary operators	__neg__-, __pos__ +, __abs__ abs ()
Many comparison operators	__lt__ <, __le__ <=, __eq__ = =, __ne__! =, __gt__ >, __ge__ >=
Arithmetic operators	__add__ +, __sub__-, __mul__ *, __truediv__/, __floordiv__//, __mod__%, __divmod__ divmod (), __pow__ * * or POW (), __roun D__ round ()
Inverse arithmetic operator	__radd__, __rsub__, __rmul__, __rtruediv__, __rfloordiv__, __rmod__, __rdivmod__, __rpow__
Incremental assignment arithmetic operators	__iadd__, __isub__, __imul__, __itruediv__, __ifloordiv__, __imod__, __ipow__
Bitwise operators	__invert__ ~, __lshift__ <<, __rshift__ >>, __and__ &, __or__ |, __xor__ ^
Inverse bitwise operators	__rlshift__, __rrshift__, __rand__, __rxor__, __ror__
Increment Assignment bitwise operator	__ilshift__, __irshift__, __iand__, __ixor__, __ior__

Python Special Methods-Special method