python?函數(shù)、變量中單下劃線和雙下劃線的區(qū)別詳解

更新時(shí)間：2023年01月18日 16:13:10 作者：岳來(lái)

本文主要介紹了python?函數(shù)、變量中單下劃線和雙下劃線的區(qū)別詳解，文中通過(guò)示例代碼介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價(jià)值，需要的朋友們下面隨著小編來(lái)一起學(xué)習(xí)學(xué)習(xí)吧

一、_func 單下劃線開(kāi)頭 --口頭私有變量

1.1、在模塊中使用單下劃線開(kāi)頭

在Python中，通過(guò)單下劃線_來(lái)實(shí)現(xiàn)模塊級(jí)別的私有化，變量除外。一般約定以單下劃線開(kāi)頭的函數(shù)為模塊私有的，也就是說(shuō)from moduleName import * 將不會(huì)引入以單下劃線開(kāi)頭的函數(shù)。模塊中使用單下劃線開(kāi)頭定義函數(shù)、全局變量和類均適用，但可以用：from module import _func形式單獨(dú)導(dǎo)入。

實(shí)例如下:

lerarn_under_line.py

# coding=utf-8
course = "math"
_credit = 4


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


def _call_var():
? ? print "帶下劃線course:%s" % course
? ? print "帶下劃線_credit:%d" % _credit


def __call_var():
? ? print "帶雙下劃線course:%s" % course
? ? print "帶雙下劃線_credit:%d" % _credit

import lerarn_under_line

>>> import lerarn_under_line
>>> lerarn_under_line.call_var
<function call_var at 0x10aa61850>
>>> lerarn_under_line.call_var()
course:math
_credit:4
>>> lerarn_under_line._call_var() ? # 單下劃線可以調(diào)用
帶下劃線course:math
帶下劃線_credit:4
>>> >>> lerarn_under_line.__call_var() ? # 雙下劃線不可調(diào)用
Traceback (most recent call last):
? File "<stdin>", line 1, 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 1, in <module>
NameError: name '_credit' is not defined
>>> call_var()
course:math
_credit:4
>>> _call_var()
Traceback (most recent call last):
? File "<stdin>", line 1, in <module>
NameError: name '_call_var' is not defined
>>> __call_var()
Traceback (most recent call last):
? File "<stdin>", line 1, 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
4
>>> from lerarn_under_line import call_var
>>> call_var()
course:math
_credit:4
>>> from lerarn_under_line import _call_var
>>> _call_var()
帶下劃線course:math
帶下劃線_credit:4
>>> from lerarn_under_line import __call_var
>>> __call_var()
帶雙下劃線course:math
帶雙下劃線_credit:4

1.2、在類中使用單下劃線開(kāi)頭

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 為%d" % (self.name, 4)
? ? ? ? else:
? ? ? ? ? ? print "%s的credit 為%d" % (self.name, 2)

? ? def _credit(self):
? ? ? ? if self.name == 'math':
? ? ? ? ? ? print "%s的credit 為%d" % (self.name, 4)
? ? ? ? else:
? ? ? ? ? ? print "%s的credit 為%d" % (self.name, 2)

? ? def __credit(self):
? ? ? ? if self.name == 'math':
? ? ? ? ? ? print "%s的credit 為%d" % (self.name, 4)
? ? ? ? else:
? ? ? ? ? ? print "%s的credit 為%d" % (self.name, 2)

import lerarn_under_line

>>> import lerarn_under_line
>>> a=Course('math')
Traceback (most recent call last):
? File "<stdin>", line 1, 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 為4
>>> a._credit()
math的credit 為4
>>> a.__credit()
Traceback (most recent call last):
? File "<stdin>", line 1, 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 1, in <module>
AttributeError: 'Course' object has no attribute '__credit'
>>> a._credit()
math的credit 為4
>>> a.credit()
math的credit 為4

綜上，單下劃線開(kāi)頭的函數(shù)表示是口頭實(shí)例私有變量，是可訪問(wèn)的，但是也不要隨意訪問(wèn)，即所謂防君子不防小人。

二、__func 雙下劃線開(kāi)頭的函數(shù) --私有變量

2.1、在模塊中使用雙下劃線開(kāi)頭

在實(shí)例中，帶雙下劃線的類變量、實(shí)例變量、方法不能被直接訪問(wèn)。但有辦法間接訪問(wèn)。如1.1中的from module import __func

>>> from lerarn_under_line import *
>>> __call_var()
Traceback (most recent call last):
? File "<stdin>", line 1, in <module>
NameError: name '__call_var' is not defined

>>> import lerarn_under_line
>>> lerarn_under_line.__call_var() ? # 雙下劃線不可調(diào)用
Traceback (most recent call last):
? File "<stdin>", line 1, 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()
帶雙下劃線course:math
帶雙下劃線_credit:4

2.2、在類中使用雙下劃線開(kāi)頭

在class類的內(nèi)部，帶雙下劃線的類變量、實(shí)例變量、方法具有正常訪問(wèn)權(quán)限。
在繼承結(jié)構(gòu)中，帶雙下劃線的基類的類變量和實(shí)例變量不能被子類直接訪問(wèn)。

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') ?# 無(wú)法實(shí)例化
Traceback (most recent call last):
? File "<stdin>", line 1, 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 1, in <module>
? File "lerarn_under_line.py", line 77, in <module>
? ? b = SonCourse('math', 'zhangyu', 'juyiting', "12：00")
? File "lerarn_under_line.py", line 63, 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 1, in <module>
? File "lerarn_under_line.py", line 77, in <module>
? ? b = SonCourse('math', 'zhangyu', 'juyiting', "12：00")
? File "lerarn_under_line.py", line 63, 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 1, in <module>
? File "lerarn_under_line.py", line 77, in <module>
? ? b = SonCourse('math', 'zhangyu', 'juyiting', "12：00")
? File "lerarn_under_line.py", line 63, 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 1, in <module>
? File "lerarn_under_line.py", line 77, in <module>
? ? b = SonCourse('math', 'zhangyu', 'juyiting', "12：00")
? File "lerarn_under_line.py", line 63, in __init__
? ? self.__classroom = self.__classroom
AttributeError: 'SonCourse' object has no attribute '_SonCourse__classroom'

三、前后都有雙下劃線 --特殊變量

Python保留了有雙前導(dǎo)和雙末尾下劃線的名稱，用于特殊用途。這樣的例子有，init__對(duì)象構(gòu)造函數(shù)，或__call — 它使得一個(gè)對(duì)象可以被調(diào)用。這些方法通常被稱為神奇方法，最好避免在自己的程序中使用以雙下劃線開(kāi)頭和結(jié)尾的名稱，以避免與將來(lái)Python語(yǔ)言的變化產(chǎn)生沖突。

常見(jiàn)方法：

方法	含義
__str__	當(dāng)將對(duì)象轉(zhuǎn)換成字符串時(shí)會(huì)執(zhí)行
__init__	初始化方法，為對(duì)象變量賦值
__new__	構(gòu)造方法，創(chuàng)建一個(gè)對(duì)象
__call__	在對(duì)象后面加括號(hào)會(huì)執(zhí)行該方法
__getattr__	當(dāng)使用對(duì)象.屬性時(shí)，若屬性不存在會(huì)調(diào)用該方法
__setattr__	當(dāng)使用對(duì)象.屬性 = 值，會(huì)調(diào)用該方法
__iter__	類內(nèi)部定義了該方法，對(duì)象就變成了可迭代對(duì)象
__add__	當(dāng)兩個(gè)對(duì)象使用+號(hào)會(huì)調(diào)用該方法
__enter__和__exit__	上下文管理

參考文檔

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

到此這篇關(guān)于python 函數(shù)、變量中單下劃線和雙下劃線的區(qū)別詳解的文章就介紹到這了,更多相關(guān)python 單下劃線和雙下劃線區(qū)別內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

您可能感興趣的文章: