Python基于locals返回作用域字典

英文文档：

locals()

Update and return a dictionary representing the current local symbol table. Free variables are returned by locals()when it is called in function blocks, but not in class blocks.

　　返回当前作用域内的局部变量和其值组成的字典

说明：

　　1. 函数功能返回当前作用域内的局部变量和其值组成的字典，与globals函数类似(返回全局变量)

>>> locals()
{'__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, '__doc__': None, '__name__': '__main__', '__builtins__': <module 'builtins' (built-in)>, '__spec__': None}

>>> a = 1

>>> locals() # 多了一个key为a值为1的项
{'__package__': None, '__loader__': <class '_frozen_importlib.BuiltinImporter'>, 'a': 1, '__doc__': None, '__name__': '__main__', '__builtins__': <module 'builtins' (built-in)>, '__spec__': None}

　　2. 可用于函数内。

>>> def f():
  print('before define a ')
  print(locals()) #作用域内无变量
  a = 1
  print('after define a')
  print(locals()) #作用域内有一个a变量，值为1
>>> f
<function f at 0x03D40588>
>>> f()
before define a 
{} 
after define a
{'a': 1}

　　3. 返回的字典集合不能修改。

>>> def f():
  print('before define a ')
  print(locals()) # 作用域内无变量
  a = 1
  print('after define a')
  print(locals()) # 作用域内有一个a变量，值为1
  b = locals()
  print('b["a"]: ',b['a']) 
  b['a'] = 2 # 修改b['a']值
  print('change locals value')
  print('b["a"]: ',b['a'])
  print('a is ',a) # a的值未变

  
>>> f()
before define a 
{}
after define a
{'a': 1}
b["a"]: 1
change locals value
b["a"]: 2
a is 1
>>>

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