The python function: Two

This paper starts from the following aspects to learn more about python function:

1. The function of variable scope
2. Closures phenomenon in the function
3. Function decorator
4. Standard library decorator
5. Superposition decorator
6. Parametric Decorator

def A(func):

　　def B():

　　　　　return 

　　return B

LEGB principle function of: the local scope -> External Scope -> global scope -> this can be a ...

 

　　　　　　For the function B function body B is called local scope, function A body called the outer scope of B, where A file is of global scope B

　　　　　　If you need to make changes in the global variables q B, please use the global keyword to declare variables

Function closure:

　　　　For the body B can call the function variable c in A defined scoping behavior is called closure criteria: a function in a non-global scope able to remember it was named the closed space (B enclosed in A)

　　　　Wherein the variables called a free variable Cc: unbound variable domain refers to the local action q using nonlocal variables to declare a free (as global)

 　　　　

Decorator:

　　　　Definition: to enhance the function of the behavior of another function execution l before the objective function objective function is modified

　　　　Performance: ex is shaped like a decorator

　　　　Use: @A

　　　　　　　def target():

　　　　　　　　　　pass

 

Parameterized decorator: the decorator know the objective function accepts a function name as a parameter is passed, then how do garnished if the objective function with parameters?

　　　　　　　A layer outside the decorator nested function, the objective function to the processing parameters of the problem

　　　　　　　　def add(*args,**kwargs):

　　　　　　　　　　def A(func):

　　　　　　　　　　　　def B(*args,**kwargs):

　　　　　　　　　　　　　　return res

　　　　　　　　　　　　return B

　　　　　　　　　　return A

　　　　　　　　Wherein the add function g c factory function call, the parameters dedicated to handling the objective function

Standard library decorator:

　　　　functools.lru_cache lru_cache which is least recently used for a function recently executed to make a record to avoid duplication of execution  　　

　　　　　　　　Memo function is to greatly simplify the running time

　　　　Single-point distribution functools.singledispatch d 

　　　　　　　　This design is also reflected in the z mode and REST frameworkz Djangoh mode of CBV

　　　　　　　　The set of functions to perform the same type of the first parameter in different ways

　　　　　　　　(Multiple dispatch: selecting a plurality of parameters according to specific functions)