> 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}

> 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}

> 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
>