Python decorator

Record python The function of ornaments , Often forget this , I can't recall , It must be because you use less .

Let's start with a simple decorator example

from functools import wraps
def other_fun(func):
print(" Start execution other_fun")
@wraps(func)
def warrp():
print(" Start execution warrp")
func()
print(" After execution warrp")
return warrp
@other_fun
def myfun():
print("myfun")
myfun()
Print the results ：
Start execution other_fun
Start execution warrp
myfun
After execution warrp

A simple decorator is equivalent to a function myfun() It is said that other_fun() perform
myfun = other_fun(myfun)

1. Essence of decorator , Or from the code structure , It can be considered as a closure
2. It's all using Python Functions themselves can be nested 、 You can also accept function parameters 、 You can also return the characteristics of a function
3. Only closures tend to take advantage of the memory resident feature , Decorators tend to take advantage of the characteristics of function return functions

We can think of a closure as a special function , This function consists of two nested functions ,
They are called external functions and internal functions , The return value of an outer function is a reference to an inner function , So that's the closure .

The second example above , Parameter decorator

# Do not use decorators 
def other_fun(func):
print(" Start execution other_fun")
def warrp(num):
print(" Start execution warrp")
result = func(num)
print(" After execution warrp")
return print(result)
return warrp
def myfun(num):
print("myfun")
return num
test = other_fun(myfun)
test(101)
Start execution other_fun
Start execution warrp
myfun
After execution warrp
101

We have seen an example of closures and function arguments , So the decorator
It's actually a closure + Function arguments , If you understand the above example , Now you just need to change the code format a little , It becomes a decorator
The syntax is more concise and beautiful when executed

# Use decorators 
def other_fun(func):
print(" Start execution other_fun")
@wraps(func)
def warrp(*args):
print(" Start execution warrp")
result = func(*args)
print(" After execution warrp")
return print(result ) #result = 101
return warrp
@other_fun
def myfun(num):
print("myfun")
return num
myfun(101)
Start execution other_fun
Start execution warrp
myfun
After execution warrp
101

By introducing functools Methods wraps, Ensure the primitive and integrity of the original function
@wraps Accept a function , Decorate , And added the copy function name 、 Annotation document 、 Parameter list and other functions , In this way, we can access the properties of the function before decoration in the decorator

Application of decorator , logging
... To be continued