python的namespace的理解

Posted 2021-12-22 tombombadil

Python命名空间的本质

 

python中的名称空间是名称(标识符)到对象的映射。

具体来说，python为模块、函数、类、对象保存一个字典(__dict__)，里面就是重名称到对象的映射。

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import urllib

import re

x=1 # 变量

def abc(): # 函数

pass

def qq(self): # 方法

pass

class typ(object): # 类

"""docstring for typ"""

def __init__(self, arg):

super(typ, self).__init__()

self.arg = arg

def classqq(self): # 不存在于全局变量中

pass

 

print(globals().keys()) # 打印字典中的key值

print()

print(globals()) # 打印全局变量，打印出来是以字典的形式展示

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dict_keys([‘__name__‘, ‘__doc__‘, ‘__package__‘, ‘__loader__‘, ‘__spec__‘, ‘__annotations__‘, ‘__builtins__‘, ‘__file__‘, ‘__cached__‘, ‘urllib‘, ‘re‘, ‘x‘, ‘abc‘, ‘qq‘, ‘typ‘])

 

‘__name__‘: ‘__main__‘, ‘__doc__‘: None, ‘__package__‘: None, ‘__loader__‘: <_frozen_importlib_external.SourceFileLoader object at 0x0000000001DEC048>, ‘__spec__‘: None, ‘__annotations__‘: , ‘__builtins__‘: <module ‘builtins‘ (built-in)>, ‘__file__‘: ‘D:\\\\Learn\\\\practice\\\\case1.py‘, ‘__cached__‘: None, ‘urllib‘: <module ‘urllib‘ from ‘D:\\\\Programs\\\\Python\\\\Python36\\\\lib\\\\urllib\\\\__init__.py‘>, ‘re‘: <module ‘re‘ from ‘D:\\\\Programs\\\\Python\\\\Python36\\\\lib\\\\re.py‘>, ‘x‘: 1, ‘abc‘: <function abc at 0x00000000001F2E18>, ‘qq‘: <function qq at 0x00000000021FAAE8>, ‘typ‘: <class ‘__main__.typ‘>

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x=1 # 变量

def abc(): # 函数

pass

def qq(self): # 方法

pass

class Typ(object): # 类

"""docstring for typ"""

k=1 # 私有变量没有被init初始化

def __init__(self):

super(Typ, self).__init__()

self.y = 2

self.z = 3

def func(self): # 函数方法不存在于全局命名空间中

print("abcd") # 函数方法会默认return None

func.fx = 2

 

test1 = Typ()

print(Typ.__dict__)

print(test1.__dict__)

print(test1.func.__dict__)

print(globals().keys())

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‘__module__‘: ‘__main__‘, ‘__doc__‘: ‘docstring for typ‘, ‘k‘: 1, ‘__init__‘: <function Typ.__init__ at 0x00000000029007B8>, ‘func‘: <function Typ.func at 0x0000000002900840>, ‘__dict__‘: <attribute ‘__dict__‘ of ‘Typ‘ objects>, ‘__weakref__‘: <attribute ‘__weakref__‘ of ‘Typ‘ objects>

‘y‘: 2, ‘z‘: 3

‘fx‘: 2

dict_keys([‘__name__‘, ‘__doc__‘, ‘__package__‘, ‘__loader__‘, ‘__spec__‘, ‘__annotations__‘, ‘__builtins__‘, ‘__file__‘, ‘__cached__‘, ‘urllib‘, ‘re‘, ‘x‘, ‘abc‘, ‘qq‘, ‘Typ‘, ‘test1‘])

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https://blog.csdn.net/u012436149/article/details/72819539

locals

内置函数locals(), 返回当前函数（方法）的局部命名空间

def function(a=1):

b=2

print(locals())

return a+b

print(function())

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‘b‘: 2, ‘a‘: 1

3

globals

内置函数globals()，返回当前module的命名空间

def function(a=1):

b=2

print(locals())

return a+b

print(function())

print(globals().keys())

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‘b‘: 2, ‘a‘: 1

3

dict_keys([‘__name__‘, ‘__doc__‘, ‘__package__‘, ‘__loader__‘, ‘__spec__‘, ‘__annotations__‘, ‘__builtins__‘, ‘__file__‘, ‘__cached__‘, ‘urllib‘, ‘re‘, ‘function‘])

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locals()和globals()有一个区别是，locals只读，globals可以写

 

from module import 和 import module

• 使用import module时，module本身被引入，但是保存它原有的命名空间，所以我们需要使用module.name这种方式访问它的 函数和变量。
• from module import这种方式，是将其它模块的函数或者变量引到当前的命名空间中，所以就不需要使用module.name这种方式访问其它的模块的方法了。