Python Learning---Object-oriented learning [in-depth]

in-depth learning of classes

A. all things in Python are objects

B. class Foo:

Pass

obj = Foo ()

# obj is an object, Foo class

# Foo class is also an object, type objects

c. classes are objects of type class type (..)

"Object" is a Class object class ()

D. class is actually an object of type types, all classes are subclasses of object

Methods for creating a class [2 kinds]

# First: The class is actually an object of type types, all classes are subclasses of object foo = type (' foo ', (object,), {' Func ': ' function '}) # Second: Class Foo:    def func ( Self):        print (123) F = Foo () f.func ()

Create a class with Metaclass: You must inherit the type class, and Init must pass 4 arguments past

You must inherit the type class   ---code is wrong---class MyType (type): # The Metaclass of a derived class must be a (non-strict) subclass of the meta Classes of all its bases    # must give 4 parameters    def __init__ (self, *args,  **kwargs):  # __init__ () takes 1 positional a Rgument but 4 were given        print (' MyType Create Class object ')    def __call__ (self, *args,  **kwargs):          print (' MyType's Call method ')    def __new__ (self, *args,  **kwargs):          print (' MyType's New method ') class Foo (object, Metaclass =mytype):    def func (self):        print (123)   # Executes the Init method after creating   the object Def __new__ (self, *args, **kwargs):       Print (' Foo's New method ')       returns ' The object of foo ' F = foo ()   # call MyType's __init__ method, Foo is the MyType object, and foo () calls MyType __call_ _ Method F.func ()    # MyType Create Class object, here is MyType            # 123

Schematic diagram of the "Reprint" class:

Exception Handling

Passive exception

Try:    passexcept indentationerror as E:    passexcept valueerror as E:  # Small exception put in front    of exception Passexcept Exception as E:   # E is a Exception object that encapsulates the Exception information    passelse:                    # Normal code is normal, then else is executed, otherwise     else passfinally:    Pass                 # Error not error, be sure to execute the code

Active Trigger exception: raise Exception ("Sorry")

Try:    raise Exception ("Sorry") except Exception as E:    print (e)

Custom Exception: inherits the exception class to implement

Class HhH (Exception):    def __init__ (self, msg):        self.message = msg    def __str__ (self):        return  Self.message   # Here you just need to return it, can't print try:    raise HhH (' HhH, wrong ') except HhH as E:    print (e)

assert assert

Assert comparison content: The condition is established, then print XXX, otherwise error

Generally with mandatory user's obedience, Java has added this feature since 1.2, but it is not usually used in practice. Python source code useful to

Assert 1 < 5print (' HHH ')

Reflection

1. Manipulating the members of an object via a string (method, field):

Class Foo:    def __init__ (self, Name, age):        self.name = name        Self.age = Age    def fun (self):        print ('%s- %s '% (Self.name, self.age)) obj = Foo (' FTL ', total) print (obj.name) b = ' name ' Print (' obj.__dict__[b]: ', obj.__dict__[b])   # Value Print via dictionary ("GetAttr (obj, ' name '):", GetAttr (obj, ' name '))  # Fetch value via built-in function getattr = getattr (obj, ' fun ') fun () SetAttr (obj, ' school ', ' Xupt ') print (hasattr (obj, ' School ')) print (Delattr (obj, ' School '))

Module-Level Reflection:

Class Foo ():    NAME = ' FTL '    def hello (self):        print (' Hello ') print (GetAttr (foo, ' NAME ')) Hello = GetAttr (foo () , ' Hello ')     # takes the memory address of the function print (hello) print (hello ())                      # takes the object to the function

single-case mode

Class Foo:    __instance = None    def __init__ (self, Name, age):        Self.age = age        self.name = name    @ Classmethod                          # static method    def get_instance (CLS):        if cls.__instance:            return cls.__instance        else:            Cls.__instance = Foo (' hhh ', +)            return cls.__instance    def show (self):        print (self.age, self.name) obj = Foo.get_instance () obj.show ()

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Python Learning---Object-oriented learning [in-depth]