Detailed explanation of LEGB, closures and decorators in Python

This article mainly introduces the detailed information about LEGB, closures and decorators in Python. It mainly introduces the understanding and use of function scope and closures and the decorators in Python. Friends who need it can refer to it.

Detailed explanation of LEGB, closures and decorators in Python

LEGB L>E>G?B

• ##L: Internal scope of local function

• E: Between the internal scope of enclosing function and embedded function

• G: Global global scope Domain

• B:build-in built-in scope

python closure

1. Closure: Reference to the enclosing scope variable in the internal function

2. Function essence and attributes

• The function is an object

• Internal variables are recycled after the function execution is completed

• Function attributes

• Function return value

  
  

passline = 60
def func(val):
  if val >= passline:
    print ('pass')
  else:
    print ('failed')
  def in_func():
    print (val)
  in_func()
  return in_func

f = func(89)
f()
print (f.__closure__)

General situation

def f_100(val):
  passline = 60
  if val >= passline:
    print ('pass')
  else:
    print ('failed')

def f_150(val):
  passline = 90
  if val >= passline:
    print ('pass')
  else:
    print ('failed')

f_100(89)
f_150(89)

Closure

def set_passline(passline):
  def cmp(val):
    if val >= passline:
      print ('Pass')
    else:
      print ('failed')
  return cmp

f_100 = set_passline(60)
f_150 = set_passline(90)
f_100(89)
f_150(89)

Closure: A reference to the enclosing scope variable in the internal function, which will pass the enclosing scope variable to the closure of the internal function

The role of closure:

• Encapsulation

• Code reuse

  
  

##python closure two

Sum

def my_sum(*arg):
  if len(arg) == 0:
    return 0
  for val in arg:
    if not isinstance(val,int): # 有一个非int则返回0
      return 0
  return sum(arg)

def my_average(*arg):
  if len(arg) == 0:
    return 0
  for val in arg:
    if not isinstance(val,int): # 有一个非int则返回0
      return 0
  return sum(arg)/len(arg)

print (my_sum(1,2,3,4,5))
print (my_sum(1,2,3,4,5,'6'))
print (my_aveage(1,2,3,4,5))
print(my_average())

Use of closure

def my_sum(*arg):
  return sum(arg)
def my_average(*arg):
  return sum(arg)/len(arg)

def dec(func):
  def in_dec(*arg): # my_sum
    print ('in dec arg= ',arg)
    if len(arg) ==0:
      return 0
    for val in arg:
      if not isinstance(val, int):
        return 0
    return func(*arg)  # 闭包，存在于in_dec函数中的__closure__中，所以可以调用
  return in_dec

my_sum = dec(my_sum)  # 传参

print(my_sum (1,2,3,4,5)）
print(my_sum (1,2,3,4,5,'6')）
# my_sum就是in_dec函数，会先执行参数类型判断，然后执行__closure__中的函数my_sum

python Decorator

Decorator is used to decorate functions
Returns a function object

2. ## The decorated function identifier points to the returned function object

3. Syntactic sugar@deco

4. 
   

   How to use the decorator

def dec(func):
  def in_dec(*arg): # my_sum
    print ('in dec arg= ',arg)
    if len(arg) ==0:
      return 0
    for val in arg:
      if not isinstance(val, int):
        return 0
    return func(*arg)  # 闭包，存在于in_dec函数中的__closure__中，所以可以调用
  return in_dec  # 如果没有返回值，则my_sum调用装饰器后为None
# my_sum = dec(my_sum)  # 不手动传参
@dec     # 装饰器将my_sum作为参数传入dec，并返回一个新的函数赋值给my_sum
def my_sum(*arg):
  return sum(arg)
def my_average(*arg):
  return sum(arg)/len(arg)
print(my_sum (1,2,3,4,5))
print(my_sum (1,2,3,4,5,'6'))

Another example

def deco(func):
  def in_deco(x,y):
    print ('in deco')
    func(x,y)
  print ('call deco')
  return in_deco
@deco
def bar(x, y):
  print ('in bar',x+y)
bar(1,2)

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