Python-a prelude to decorators

If you want to learn what a decorator is, you must first know the composition of a decorator. It can be said that a decorator is composed of the following three aspects:

Scope

Speaking of scope, it is actually the search order of L_E_G_B in Python. Look at the code.

 a = abs(-2)              #abs是Python内置的函数，其实这时的abs()就相当于是一个built-in变量
 b = 3            #这就相当于是一个global变量
 def one_function():
     c = 1                #这就是一个enclosing变量
     def two_function():
             d = -1        #这就是一个local变量
             e = c+b
             return e

#比如说在函数two_function中，变量d中调用b,就会先在自身的函数中查找b这个变量，如果未查找到，则会进入上一层函数中进行查找，即one_function函数中查找b这个变量。

#查找到时被调用.如果未查找到，则会进入全局变量进行查找.

The second aspect about decorators is about higher-order functions

Higher order function

First, let’s talk about the conditions of higher-order functions:

1. The function name can be assigned.

2. The function name can be used as a function parameter or as the return value of the function.

#首先创建一个函数

 def add(x,y,f):
     return f(x)+f(y)

#然后我们调用这个函数
 add(-5,9,abs)              #14

#等价于abs(-5)+abs(9)

Closure

Next, let’s talk about closures

#接下来说一说闭包，首先我们创建一个函数
 def foo3():
     def inner():
             return 8
     return inner

#在这个函数中，我们如何得到8这个值呢，
 foo3()()
8
 inner()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'inner' is not defined

Python-a prelude to decorators

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