Talking about the name of the variable or function with _ in Python, talking about python

Talking about the name of the variable or function with _ in Python, talking about python

The Python code style is described by PEP 8. This document describes all aspects of the Python programming style. By following this document, the Python code written by different programmers can maintain the most similar style. This makes it easy to read and communicate with programmers.

An identifier in python can contain numbers, letters, and underscores (_), but must start with a letter or underscore (_). The name starting with underscore (_) has special meanings.

Names with double underscores (_)

It is generally used for naming special methods to implement some behaviors or functions of objects. For example, the _ new _ () method is used to create an instance, and the __init _ () method is used to initialize objects,

The x + y operation is mapped to method x. _ add _ (y), sequence or dictionary index operations x [k] ing to x. _ getitem _ (k) ,__ len _ () and _ str _ () are called by built-in functions len () and str () respectively.

Only names with double underscores (_)

Used for Object Data encapsulation. The attributes or methods named in this form are private attributes or private methods of the class.

class Foo(object):  def __init__(self):    self.__name = 'private name'   def getname(self):    return self.__name   def __spam(self):    print 'private method'   def bar(self):    self.__spam()

If you directly access private properties or methods externally:

>>> f = Foo()>>> f.__name Traceback (most recent call last): File "<pyshell#1>", line 1, in <module>  f.__nameAttributeError: 'Foo' object has no attribute '__name'>>> f.__spam() Traceback (most recent call last): File "<pyshell#2>", line 1, in <module>  f.__spam()AttributeError: 'Foo' object has no attribute '__spam'

It is not feasible, which plays a role in hiding data. However, this implementation mechanism is not very strict and is implemented through automatic "deformation, all _ names starting with double underscores in the class are automatically changed to a new name of "_ class name_name:

>>> f._Foo__name'private name'>>> f._Foo__spam()private method

In this way, you can access it.

This mechanism can prevent the inheritance class from being redefined or changing the implementation of the method, for example, defining a Foo derived class:

class Goo(Foo):  def __spam(self):    print 'private method of Goo'

Override the _ spam method and run:

>>> g = Goo()>>> g.bar()private method

When calling the bar () method, the _ spam () method of the Foo class is still executed, because in the implementation of the bar () method, self. _ spam () is automatically deformed to self. the same applies to the bar () method inherited by _ Foo _ spam () and Goo.

Name starting with an underscore _

It is generally used for the name defined by "private" in the module.

The from module import * statement is used to load all the names in the module. To control the import name, define the LIST _ all __, only the names in _ all _ can be imported through,

Another method is to name a definition starting with a single underline. This definition will not be imported.

Of course, you can also name attributes or methods with a single underline in the class. This only indicates that the class definer wants these attributes or methods to be "private ", but it does not actually play any role.

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