python 函数、变量中单下划线和双下划线的区别详解

一、_func 单下划线开头 --口头私有变量
1.1、在模块中使用单下划线开头
1.2、在类中使用单下划线开头
二、__func 双下划线开头的函数 --私有变量
2.1、在模块中使用双下划线开头
2.2、在类中使用双下划线开头
三、前后都有双下划线 --特殊变量

一、_func 单下划线开头 --口头私有变量

1.1、在模块中使用单下划线开头

在Python中，通过单下划线_来实现模块级别的私有化，变量除外。一般约定以单下划线开头的函数为模块私有的，也就是说from moduleName import * 将不会引入以单下划线开头的函数。模块中使用单下划线开头定义函数、全局变量和类均适用，但可以用：from module import _func形式单独导入。

实例如下:

lerarn_under_line.py

 
# coding=utf-
course = "math"
_credit =
 
 
def call_var():
    print "course:%s" % course
    print "_credit:%d" % _credit
 
 
def _call_var():
    print "带下划线course:%s" % course
    print "带下划线_credit:%d" % _credit
 
 
def __call_var():
    print "带双下划线course:%s" % course
    print "带双下划线_credit:%d" % _credit

import lerarn_under_line

 
>>> import lerarn_under_line
>>> lerarn_under_line.call_var
<function call_var atx10aa61850>
>>> lerarn_under_line.call_var()
course:math
_credit:
>>> lerarn_under_line._call_var()   # 单下划线可以调用
带下划线course:math
带下划线_credit:
>>> >>> lerarn_under_line.__call_var()   # 双下划线不可调用
Traceback (most recent call last):
  File "<stdin>", line, in <module>
AttributeError: 'module' object has no attribute '__call_var'

from lerarn_under_line import *

 
>>> from lerarn_under_line import *
>>> course
'math'
>>> _credit
Traceback (most recent call last):
  File "<stdin>", line, in <module>
NameError: name '_credit' is not defined
>>> call_var()
course:math
_credit:
>>> _call_var()
Traceback (most recent call last):
  File "<stdin>", line, in <module>
NameError: name '_call_var' is not defined
>>> __call_var()
Traceback (most recent call last):
  File "<stdin>", line, in <module>
NameError: name '__call_var' is not defined

from module import _func

 
>>> from lerarn_under_line import course
>>> course
'math'
>>> from lerarn_under_line import _credit
>>> _credit
>>> from lerarn_under_line import call_var
>>> call_var()
course:math
_credit:
>>> from lerarn_under_line import _call_var
>>> _call_var()
带下划线course:math
带下划线_credit:
>>> from lerarn_under_line import __call_var
>>> __call_var()
带双下划线course:math
带双下划线_credit:

1.2、在类中使用单下划线开头

lerarn_under_line.py

 
class Course(object):
    def __init__(self, name):
        self.name = name
 
    def credit(self):
        if self.name == 'math':
            print "%s的credit 为%d" % (self.name,)
        else:
            print "%s的credit 为%d" % (self.name,)
 
    def _credit(self):
        if self.name == 'math':
            print "%s的credit 为%d" % (self.name,)
        else:
            print "%s的credit 为%d" % (self.name,)
 
    def __credit(self):
        if self.name == 'math':
            print "%s的credit 为%d" % (self.name,)
        else:
            print "%s的credit 为%d" % (self.name,)

import lerarn_under_line

 
>>> import lerarn_under_line
>>> a=Course('math')
Traceback (most recent call last):
  File "<stdin>", line, in <module>
NameError: name 'Course' is not defined

from lerarn_under_line import *

 
>>> from lerarn_under_line import *
>>> a=Course('math')
>>> a.credit()
math的credit 为
>>> a._credit()
math的credit 为
>>> a.__credit()
Traceback (most recent call last):
  File "<stdin>", line, in <module>
AttributeError: 'Course' object has no attribute '__credit'

from lerarn_under_line import Course

 
>>> from lerarn_under_line import Course
>>> a=Course('math')
>>> a.__credit()
Traceback (most recent call last):
  File "<stdin>", line, in <module>
AttributeError: 'Course' object has no attribute '__credit'
>>> a._credit()
math的credit 为
>>> a.credit()
math的credit 为

综上，单下划线开头的函数表示是口头实例私有变量，是可访问的，但是也不要随意访问，即所谓防君子不防小人。

二、__func 双下划线开头的函数 --私有变量

2.1、在模块中使用双下划线开头

在实例中，带双下划线的类变量、实例变量、方法不能被直接访问。但有办法间接访问。如1.1中的from module import __func

 
>>> from lerarn_under_line import *
>>> __call_var()
Traceback (most recent call last):
  File "<stdin>", line, in <module>
NameError: name '__call_var' is not defined
 
>>> import lerarn_under_line
>>> lerarn_under_line.__call_var()   # 双下划线不可调用
Traceback (most recent call last):
  File "<stdin>", line, in <module>
AttributeError: 'module' object has no attribute '__call_var'
 
>>> from lerarn_under_line import course
>>> from lerarn_under_line import __call_var
>>> __call_var()
带双下划线course:math
带双下划线_credit:

2.2、在类中使用双下划线开头

在class类的内部，带双下划线的类变量、实例变量、方法具有正常访问权限。
在继承结构中，带双下划线的基类的类变量和实例变量不能被子类直接访问。

lerarn_under_line.py

 
class Course(object):
    def __init__(self, name, _teacher, __classroom):
        self.name = name
        self._teacher = _teacher
        self.__classroom = __classroom
 
    def call_var(self):
        print "name:%s" % self.name
        print "_teacher:%s" % self._teacher
        print "__classroom:%s" % self.__classroom   
>>> import lerarn_under_line
>>> a = Course('math', 'zhangyu', 'juyiting')  # 无法实例化
Traceback (most recent call last):
  File "<stdin>", line, in <module>
NameError: name 'Course' is not defined
>>> from lerarn_under_line import *
>>> a = Course('math', 'zhangyu', 'juyiting')
>>> a.call_var()
name:math
_teacher:zhangyu
__classroom:juyiting

lerarn_under_line.py

 
class Course(object):
    def __init__(self, name, _teacher, __classroom):
        self.name = name
        self._teacher = _teacher
        self.__classroom = __classroom
 
    def call_var(self):
        print "name:%s" % self.name
        print "_teacher:%s" % self._teacher
        print "__classroom:%s" % self.__classroom
 
 
class SonCourse(Course):
    def __init__(self, name, _teacher, __classroom, time):
        super(Course, self).__init__()
        self.time = time
        self.name = name
        self.__classroom = self.__classroom
        self._teacher = self._teacher
        self.__classroom = self.__classroom
 
    def call_son_var(self):
        print "time:%s" % self.time
        print "name:%s" % self.name
        print "_teacher:%s" % self._teacher
        print "__classroom:%s" % self.__classroom
>>> import lerarn_under_line
Traceback (most recent call last):
  File "<stdin>", line, in <module>
  File "lerarn_under_line.py", line, in <module>
    b = SonCourse('math', 'zhangyu', 'juyiting', "：00")
  File "lerarn_under_line.py", line, in __init__
    self.__classroom = self.__classroom
AttributeError: 'SonCourse' object has no attribute '_SonCourse__classroom'
 
>>> from lerarn_under_line import *
Traceback (most recent call last):
  File "<stdin>", line, in <module>
  File "lerarn_under_line.py", line, in <module>
    b = SonCourse('math', 'zhangyu', 'juyiting', "：00")
  File "lerarn_under_line.py", line, in __init__
    self.__classroom = self.__classroom
AttributeError: 'SonCourse' object has no attribute '_SonCourse__classroom'
 
>>> from lerarn_under_line import Course
Traceback (most recent call last):
  File "<stdin>", line, in <module>
  File "lerarn_under_line.py", line, in <module>
    b = SonCourse('math', 'zhangyu', 'juyiting', "：00")
  File "lerarn_under_line.py", line, in __init__
    self.__classroom = self.__classroom
AttributeError: 'SonCourse' object has no attribute '_SonCourse__classroom'
 
>>> from lerarn_under_line import sonCourse
Traceback (most recent call last):
  File "<stdin>", line, in <module>
  File "lerarn_under_line.py", line, in <module>
    b = SonCourse('math', 'zhangyu', 'juyiting', "：00")
  File "lerarn_under_line.py", line, in __init__
    self.__classroom = self.__classroom
AttributeError: 'SonCourse' object has no attribute '_SonCourse__classroom'

三、前后都有双下划线 --特殊变量

Python保留了有双前导和双末尾下划线的名称，用于特殊用途。这样的例子有，init__对象构造函数，或__call — 它使得一个对象可以被调用。这些方法通常被称为神奇方法，最好避免在自己的程序中使用以双下划线开头和结尾的名称，以避免与将来Python语言的变化产生冲突。

常见方法：

方法	含义
__str__	当将对象转换成字符串时会执行
__init__	初始化方法，为对象变量赋值
__new__	构造方法，创建一个对象
__call__	在对象后面加括号会执行该方法
__getattr__	当使用对象.属性时，若属性不存在会调用该方法
__setattr__	当使用对象.属性 = 值，会调用该方法
__iter__	类内部定义了该方法，对象就变成了可迭代对象
__add__	当两个对象使用+号会调用该方法
__enter__和__exit__	上下文管理

参考文档

1、https://blog.csdn.net/brucewong0516/article/details/79120841

2、http://t.zoukankan.com/one-tom-p-11749739.html

3、https://www.cnblogs.com/bryant24/p/11429653.html

4、https://blog.csdn.net/m0_58357932/article/details/121062461

5、https://www.likecs.com/show-308380836.html

	# coding=utf-
	course = "math"
	_credit =


	def call_var():
	print "course:%s" % course
	print "_credit:%d" % _credit


	def _call_var():
	print "带下划线course:%s" % course
	print "带下划线_credit:%d" % _credit


	def __call_var():
	print "带双下划线course:%s" % course
	print "带双下划线_credit:%d" % _credit

	>>> import lerarn_under_line
	>>> lerarn_under_line.call_var
	<function call_var atx10aa61850>
	>>> lerarn_under_line.call_var()
	course:math
	_credit:
	>>> lerarn_under_line._call_var() # 单下划线可以调用
	带下划线course:math
	带下划线_credit:
	>>> >>> lerarn_under_line.__call_var() # 双下划线不可调用
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	AttributeError: 'module' object has no attribute '__call_var'

	>>> from lerarn_under_line import *
	>>> course
	'math'
	>>> _credit
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	NameError: name '_credit' is not defined
	>>> call_var()
	course:math
	_credit:
	>>> _call_var()
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	NameError: name '_call_var' is not defined
	>>> __call_var()
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	NameError: name '__call_var' is not defined

	>>> from lerarn_under_line import course
	>>> course
	'math'
	>>> from lerarn_under_line import _credit
	>>> _credit
	>>> from lerarn_under_line import call_var
	>>> call_var()
	course:math
	_credit:
	>>> from lerarn_under_line import _call_var
	>>> _call_var()
	带下划线course:math
	带下划线_credit:
	>>> from lerarn_under_line import __call_var
	>>> __call_var()
	带双下划线course:math
	带双下划线_credit:

	class Course(object):
	def __init__(self, name):
	self.name = name

	def credit(self):
	if self.name == 'math':
	print "%s的credit 为%d" % (self.name,)
	else:
	print "%s的credit 为%d" % (self.name,)

	def _credit(self):
	if self.name == 'math':
	print "%s的credit 为%d" % (self.name,)
	else:
	print "%s的credit 为%d" % (self.name,)

	def __credit(self):
	if self.name == 'math':
	print "%s的credit 为%d" % (self.name,)
	else:
	print "%s的credit 为%d" % (self.name,)

	>>> import lerarn_under_line
	>>> a=Course('math')
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	NameError: name 'Course' is not defined

	>>> from lerarn_under_line import *
	>>> a=Course('math')
	>>> a.credit()
	math的credit 为
	>>> a._credit()
	math的credit 为
	>>> a.__credit()
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	AttributeError: 'Course' object has no attribute '__credit'

	class Course(object):
	def __init__(self, name, _teacher, __classroom):
	self.name = name
	self._teacher = _teacher
	self.__classroom = __classroom

	def call_var(self):
	print "name:%s" % self.name
	print "_teacher:%s" % self._teacher
	print "__classroom:%s" % self.__classroom
	>>> import lerarn_under_line
	>>> a = Course('math', 'zhangyu', 'juyiting') # 无法实例化
	Traceback (most recent call last):
	File "<stdin>", line, in <module>
	NameError: name 'Course' is not defined
	>>> from lerarn_under_line import *
	>>> a = Course('math', 'zhangyu', 'juyiting')
	>>> a.call_var()
	name:math
	_teacher:zhangyu
	__classroom:juyiting

python 函数、变量中单下划线和双下划线的区别详解

目录

一、_func 单下划线开头 --口头私有变量

1.1、在模块中使用单下划线开头

1.2、在类中使用单下划线开头

二、__func 双下划线开头的函数 --私有变量

2.1、在模块中使用双下划线开头

2.2、在类中使用双下划线开头

三、前后都有双下划线 --特殊变量