47. Polymorphic 多態性

• the ability to define a generic type of behavior that will (potentially) behave differently when applied to different types

• Python is very polymorphic in nature.

  1. Duck typing
     1. if it walks like a duck and quacks like a duck then it is a duck
  2. when we iterate over a collection
     1. obejct just needs to supports the iterable protocol

  It does not matter if the collection is a list, a tuple, a dictionary or a generator.

  Only care about is that it supports the iterable protocol

• +, -, *, /

  1. integer, floats, decimals, complex numbers
  2. lists, tuples
  3. custom objects

  We can add support to our own classes for the + operator by implementing:

  _ _ add _ _ method

• Special Methods

  Start double underscore and End double underscore: dunder methods.

  Never use this naming atandard for your own methods or attributes - not guarantee won’t break in the future.

  ex: _ _ my_function _ _ = (don’t use)

  “”might misunderstanding this as a python things, not a custom codes””.

• other special methods:

  _ _ init _ _

  _ _ enter _ _ : context managers, ctx( )

  _ _ getitem_ _: sequence tyoes

  _ _ iter_ _: iterables and iterators

  _ _ len _ _: implement len( )

48. / 49. _ _ str _ _ and _ _ repr _ _ Methods

both used for creating a string

_ _ repr _ _ is used by developers

1. string could be used to recreated the object
2. descriptive 描述
3. debugging
4. called when using the repr( ) function

_ _ str _ _ is used by str ( ) and print ( ), as well as various formating functions

1. typically used for display purpose to end user, logging, etc
2. if _ _ str _ _ is not implemented, Pyhton will look for _ _ repr _ _ instead

if neither is implemented and since all objects inherit from Object, will use _ _ repr _ _ defined there instead

1. Every object actually inherits from kind of a parent or grandparent object that have default inmplementation
2. class name, memory locations…