Python variable access control several methods: Single underline, double underline, __slots__, @property, __all____python

1. Single Underline:

A single underline named variables (including classes, functions, generic variables) cannot be imported into another module through the From module import *.

testa.py

# testa.py
_foo (object):
    Fun (self):
        print (' Fun in Class _foo ')
        
        
_bar (a):
    Print (a)
    

testb.py

*

a = _foo ()
_bar (' Hello World ')
C = _foobar

Testb.py will complain:

Traceback (most recent call last):
  <module>
    a = _foo ()
defined

2. Double underline:

There are no private keywords in python to control the variables of class member access, but you can achieve the same effect by naming the variable as a double underline, in the form of __xxx (not __xxx__, which has a special meaning and is accessible).

>>> class Foo (object):
	def __init__ (Self, a):
		self.__a = a
	def __fun (self):
		print (self.__a)

		
>>> t = Foo (MB)
>>> t.__fun ()
Traceback (most recent call last):
  File "<pyshell# 25> ", line 1, in <module>
    t.__fun ()
attributeerror: ' Foo ' object has no attribute ' __fun '
>> > T.__a
traceback (most recent call last):
  File "<pyshell#26>", line 1, in <module>
    t.__a< C14/>attributeerror: ' Foo ' object has no attribute ' __a '
>>>

The class itself can access the __XXX variable, but not in other scopes. The principle is that in Python the variable variable in the __xxx form of the class is restructured to _classname__xxx, so the variable in the __xxx form cannot be accessed.
In fact, it can be accessed through _classname__xxx, but not recommended, the code is as follows:

>>> class Foo (object):
	def __init__ (Self, a):
		self.__a = a
	def __fun (self):
		print (self.__a)

		
>>> t = Foo (MB)
>>> t._foo__a
100

3. __slots__: __slots__ can control the increase of class member variables, only variables appearing in __slots__ can be added to the class.

>>> class Foo ():
	__slots__ = (' name ', ' age ')
	def __init__ (self, A, b):
		self.name = a
		self.age = 1 9
		self.addr = ' i '


>>> t = Foo (' Xmr ', a)
Traceback (most recent call last):
  File "<pyshel L#68> ", line 1, in <module>
    t = Foo (' xmr ', @)
  File" <pyshell#67> ", line 6, in __init__
    SELF.A DDR = 1000
attributeerror: ' Foo ' object has no attribute ' addr '
>>>
>>> class Bar ():  c14/>__slots__ = (' name ', ' age ')
	def __init__ (self, A, b):
		self.name = a
		self.age =


		
>>> t = Bar (' xmr ',%)
>>> t.name = ' xmr '
>>> t.age = '
>>> t.addr = ' ' '
Aceback (most recent):
  File "<pyshell#76>", line 1, in <module>
    t.addr = ' the '
Ributeerror: ' Bar ' object has no attribute ' addr '
>>>

Neither class Foo nor bar in the above code can increase other member variables except name and age, because only name age is in the __slots__.

4. @property:

The role of @property is to use a member function as a variable, but the variable cannot be modified:

>>> a = Foo (MB)
>>> a.fun
>>> a.fun =
Traceback (most recent call Las T):
  File "<pyshell#97>", line 1, in <module>
    a.fun =
attributeerror:can ' t set attribute

5.__all__:

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