Function scope in Python

This article mainly introduces the function scope in Python, which has certain reference value. Now I share it with everyone. Friends in need can refer to it

In Python, a function is an effect area. This article focuses on introducing the function scope in python. Friends who are interested should take a look.

In python, a function is a scope

name = 'xiaoyafei'
def change_name():
  name = '肖亚飞'
  print('在change_name里的name:',name)
change_name() # 调用函数
print("在外面的name:",name)

The running results are as follows:

The name in change_name: Xiao Yafei
The name outside: xiaoyafei

Let’s try again how to search in the nested function ?

age = 15
def func():
  print('第一层age:',age) # 第一层age: 15
  def func2():
    age = 73
    print("func2中的age:",age) # func2中的age: 73
    def func3():
      age = 84
      print("func3中的age:",age) # func3中的age: 84
    func3() # 调用func3函数
  func2() # 调用func2函数
func()

In the above nested functions, it can be well explained that a function is a scope, so let’s change the code a little now to see the situation?

age = 15
def func():
  print('第一层age:',age) # 第一层age: 15
  def func2():
    print("func2中的age:",age) # func2中的age: 15 # 看到没有,如果当前作用域里没有age变量,那么它就会往上找
    def func3():
      age = 84
      print("func3中的age:",age) # func3中的age: 84
    func3() # 调用func3函数
  func2() # 调用func2函数
func()

So, at this time Someone said that a lot of nonsense turned out to be local variables and global variables. So I want to ask: In the above nested function, there is no age variable in func2, so how does it find the global variable age = 15? ?

At this point we need to look at the search order of the scope:

Variable scope LEGB

• L: locals The name space within the function, including local variables and actual parameters

• E: enclosing The name space of the external nested function, that is, the adjacent previous one Layer, for example: if there is no age variable in func2, it will go to func to find this

• G: globals global variable

• B: Builtins The name space of built-in modules

Ahem, let’s first understand what a name space is?

Name space, also known as name space, as the name implies, is where names are stored. Where, what name is stored? For example, x = 1, 1 is stored in the memory, then where is the variable name x stored? The name space is the place where the binding relationship between the name x and 1 is stored

>>> x = 1
>>> id(1)
1576430608

Name Spaces are divided into the following three types:

• locals: is the name space within the function, including local variables and formal parameters

• globals: global variables , the name space of the module where the function definition is located

• builtins: the name space of the built-in module

The scope of different variables is different because this variable is located Determined by the namespace.

The scope is the scope

• Global scope: global survival, global validity

• Local scope :Temporary inventory, partially valid

Let us take an example to see

level = 'L0'
n = 22
def func():
  level = 'L1'
  n = 33
  print(locals()) # {'n': 33, 'level': 'L1'} 在之前说过在python中,一个函数就是一个作用域,这就很完美的体现了
  def outer():
    n = 44
    level = 'L2'
    print(locals(),n) # {'level': 'L2', 'n': 44} 44
    def inner():
      level = 'L3'
      print(locals(),n) # {'level': 'L3', 'n': 44} 44
    inner()
  outer()
func()

L --> E --> G -->B rule Search, that is: if it is not found locally, it will be searched locally (such as closures). If it cannot be found, it will be searched globally, and then it will be searched in built-in functions.

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Introduction to functions in python

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