Python decorator usage example and practical application example

This article mainly introduces the Python decorator use examples and practical application examples. This article provides practical use examples such as the Fibonacci series, registration callback functions, mysql encapsulation, and thread asynchronization, for more information, see Test 1

Deco is running, but myfunc is not running

The code is as follows:

Def deco (func ):
Print 'Before func'
Return func

Def myfunc ():
Print 'myfunc () called'

Myfunc = deco (myfunc)

Test 2

Call myfunc in the required deco to execute

The code is as follows:

Def deco (func ):
Print 'Before func'
Func ()
Print 'after func'
Return func

Def myfunc ():
Print 'myfunc () called'

Myfunc = deco (myfunc)

Test 3

@ Function name, but it is executed twice

The code is as follows:

Def deco (func ):
Print 'Before func'
Func ()
Print 'after func'
Return func

@ Deco
Def myfunc ():
Print 'myfunc () called'

Myfunc ()

Test 4

This decoration is required.

The code is as follows:

Def deco (func ):
Def _ deco ():
Print 'Before func'
Func ()
Print 'after func'
Return _ deco

@ Deco
Def myfunc ():
Print 'myfunc () called'

Myfunc ()

Test 5

@ Use nested methods with parameters

The code is as follows:

Def deco (arg ):
Def _ deco (func ):
Print arg
Def _ deco ():
Print 'Before func'
Func ()
Print 'after func'
Return _ deco
Return _ deco

@ Deco ('demo ')
Def myfunc ():
Print 'myfunc () called'

Myfunc ()

Test 6

Function parameter transfer

The code is as follows:

Def deco (arg ):
Def _ deco (func ):
Print arg
Def _ deco (str ):
Print 'Before func'
Func (str)
Print 'after func'
Return _ deco
Return _ deco

@ Deco ('demo ')
Def myfunc (str ):
Print 'myfunc () called', str

Myfunc ('Hello ')

Test 7

Number of unknown parameters

The code is as follows:

Def deco (arg ):
Def _ deco (func ):
Print arg
Def _ deco (* args, ** kwargs ):
Print 'Before func'
Func (* args, ** kwargs)
Print 'after func'
Return _ deco
Return _ deco

@ Deco ('decode1 ')
Def myfunc1 (str ):
Print 'myfunc1 () called', str

@ Deco ('demo2 ')
Def myfunc2 (str1, str2 ):
Print 'myfunc2 () called', str1, str2

Myfunc1 ('Hello ')

Myfunc2 ('hello', 'World ')

Test 8

Class as modifier

The code is as follows:

Class myDecorator (object ):

Def _ init _ (self, fn ):
Print "inside myDecorator. _ init __()"
Self. fn = fn

Def _ call _ (self ):
Self. fn ()
Print "inside myDecorator. _ call __()"

@ MyDecorator
Def aFunction ():
Print "inside aFunction ()"

Print "Finished decorating aFunction ()"

AFunction ()

Test 9

The code is as follows:

Class myDecorator (object ):

Def _ init _ (self, str ):
Print "inside myDecorator. _ init __()"
Self. str = str
Print self. str

Def _ call _ (self, fn ):
Def wrapped (* args, ** kwargs ):
Fn ()
Print "inside myDecorator. _ call __()"
Return wrapped

@ MyDecorator ('this is str ')
Def aFunction ():
Print "inside aFunction ()"

Print "Finished decorating aFunction ()"

AFunction ()

Instance

Caching functions-Fibonacci series

The code is as follows:

From functools import wraps
Def memo (fn ):
Cache = {}
Miss = object ()

@ Wraps (fn)
Def wrapper (* args ):
Result = cache. get (args, miss)
If result is miss:
Result = fn (* args)
Cache [args] = result
Return result

Return wrapper

@ Memo
Def fib (n ):
If n <2:
Return n
Return fib (n-1) + fib (n-2)

Print fib (10)

Register callback function-web request callback

The code is as follows:

Class MyApp ():
Def _ init _ (self ):
Self. func_map = {}

Def register (self, name ):
Def func_wrapper (func ):
Self. func_map [name] = func
Return func
Return func_wrapper

Def call_method (self, name = None ):
Func = self. func_map.get (name, None)
If func is None:
Raise Exception ("No function registered against-" + str (name ))
Return func ()

App = MyApp ()

@ App. register ('/')
Def main_page_func ():
Return "This is the main page ."

@ App. register ('/next_page ')
Def next_page_func ():
Return "This is the next page ."

Print app. call_method ('/')
Print app. call_method ('/next_page ')

Mysql encapsulation-easy to use

The code is as follows:

Import umysql
From functools import wraps

Class organization AION:
Def _ init _ (self, env ):
If env = "Prod ":
Self. host = "coolshell.cn"
Self. port = 3306
Self. db = "coolshell"
Self. user = "coolshell"
Self. passwd = "fuckgfw"
Elif env = "Test ":
Self. host = 'localhost'
Self. port = 3300
Self. user = 'coolshell'
Self. db = 'coolshell'
Self. passwd = 'fuckgfw'

Def mysql (SQL ):

_ Conf = paiaion (env = "Prod ")

Def on_ SQL _error (err ):
Print err
Sys. exit (-1)

Def handle_ SQL _result (rs ):
If rs. rows> 0:
Fieldnames = [f [0] for f in rs. fields]
Return [dict (zip (fieldnames, r) for r in rs. rows]
Else:
Return []

Def decorator (fn ):
@ Wraps (fn)
Def wrapper (* args, ** kwargs ):
Mysqlconn = umysql. Connection ()
Mysqlconn. settimeout (5)
Mysqlconn. connect (_ conf. host, _ conf. port, _ conf. user ,\
_ Conf. passwd, _ conf. db, True, 'utf8 ')
Try:
Rs = mysqlconn. query (SQL ,{})
Failed T umysql. Error as e:
On_ SQL _error (e)

Data = handle_ SQL _result (rs)
Kwargs ["data"] = data
Result = fn (* args, ** kwargs)
Mysqlconn. close ()
Return result
Return wrapper

Return decorator


@ Mysql (SQL = "select * from coolshell ")
Def get_coolshell (data ):
......
.....

Asynchronous thread

The code is as follows:

From threading import Thread
From functools import wraps

Def async (func ):
@ Wraps (func)
Def async_func (* args, ** kwargs ):
Func_hl = Thread (target = func, args = args, kwargs = kwargs)
Func_hl.start ()
Return func_hl

Return async_func

If _ name _ = '_ main __':
From time import sleep

@ Async
Def print_somedata ():
Print 'starting print_somedata'
Sleep (2)
Print 'print _ somedata: 2 sec passed'
Sleep (2)
Print 'print _ somedata: 2 sec passed'
Sleep (2)
Print 'finished print_somedata'

Def main ():
Print_somedata ()
Print 'back in main'
Print_somedata ()
Print 'back in main'

Main ()