Python function decorator usage example

Python function decorator usage example

This document describes how to use the python function decorator. Share it with you for your reference. The details are as follows:

The decorator is often used in scenarios with cut-plane requirements. More typical scenarios include log insertion, performance testing, and transaction processing. The decorator is an excellent design for solving such problems,

With the decorator, we can extract a large number of identical codes irrelevant to the function itself and continue to reuse them. In summary, the purpose of the decorator is to add additional functions to existing objects.

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#! Coding = UTF-8 Import time Def timeit (func ): Def wrapper (): Start = time. clock () Func (1, 2) End = time. clock () Print 'used: ', end-start Print Return wrapper @ Timeit # Foo = timeit (foo) is equivalent, # After use, the foo function changes, which is equivalent to wrapper. Def foo (a, B ): Pass # Decorator without Parameters # Wraper will decorate fn, return wraper, and return wraper is the fn after decoration Def test (func ): Def wraper (): Print "test start" Func () Print "end start" Return wraper @ Test Def foo (): Print "in foo" Foo ()

Output:

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Test start In foo End start

Modifier with parameters:

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Def parameter_test (func ): Def wraper (): Print "test start" Func () Print "end start" Return wraper @ Parameter_test Def parameter_foo (): Print "parameter_foo:" + # Parameter_foo ('hello ')

Output:

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>>> Test start Parameter_foo: hello End start

Modifier:

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Def much_test (func ): Def wraper (* args, ** kwargs ): Print "test start" Func (* args, ** kwargs) Print "end start" Return wraper @ Much_test Def much1 (): Print @ Much_test Def much2 (a, B, c, d ): Print a, B, c, d Muyun ('A ') Much2 (1, 2, 3, 4)

Output:

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Test start A End start Test start 1 2 3 4 End start

You can package another layer of decorator with parameters:

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Def tp (name, age ): Def much_test (func ): Print 'in much_test' Def wraper (* args, ** kwargs ): Print "test start" Print str (name), 'at: '+ str (age) Func (* args, ** kwargs) Print "end start" Return wraper Return much_test @ Tp ('one', '10 ') Def tpTest (parameter ): Print parameter TpTest ('python ....')

Output:

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In much_test Test start One at: 10 Python .... End start

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Class locker: Def _ init _ (self ): Print ("locker. _ init _ () shocould be not called .") @ Staticmethod Def acquire (): Print ("locker. acquire () called. (This is a static method )") @ Staticmethod Def release (): Print ("locker. release () called. (object instance not required ") Def deco (cls ): ''' Cls must implement the acquire and release static methods ''' Def _ deco (func ): Def _ deco (): Print ("before % s called [% s]." % (func. _ name __, cls )) Cls. acquire () Try: Return func () Finally: Cls. release () Return _ deco Return _ deco @ Deco (locker) Def myfunc (): Print ("myfunc () called .") Myfunc ()

Output:

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>>> Before myfunc called [_ main _. locker]. Locker. acquire () called. (This is a static method) Myfunc () called. Locker. release () called. (The object instance is not required. >>>

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Class mylocker: Def _ init _ (self ): Print ("mylocker. _ init _ () called .") @ Staticmethod Def acquire (): Print ("mylocker. acquire () called .") @ Staticmethod Def unlock (): Print ("mylocker. unlock () called .") Class lockerex (mylocker ): @ Staticmethod Def acquire (): Print ("lockerex. acquire () called .") @ Staticmethod Def unlock (): Print ("lockerex. unlock () called .") Def lockhelper (cls ): ''' Cls must implement the acquire and release static methods ''' Def _ deco (func ): Def _ deco (* args, ** kwargs ): Print ("before % s called." % func. _ name __) Cls. acquire () Try: Return func (* args, ** kwargs) Finally: Cls. unlock () Return _ deco Return _ deco Class example: @ Lockhelper (mylocker) Def myfunc (self ): Print ("myfunc () called .") @ Lockhelper (mylocker) @ Lockhelper (lockerex) Def myfunc2 (self, a, B ): Print ("myfunc2 () called .") Return a + B If _ name __= = "_ main __": A = example () A. myfunc () Print (a. myfunc ()) Print (a. myfunc2 (1, 2 )) Print (a. myfunc2 (3, 4 ))

Output:

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Before myfunc called. Mylocker. acquire () called. Myfunc () called. Mylocker. unlock () called. Before myfunc called. Mylocker. acquire () called. Myfunc () called. Mylocker. unlock () called. None Before _ deco called. Mylocker. acquire () called. Before myfunc2 called. Lockerex. acquire () called. Myfunc2 () called. Lockerex. unlock () called. Mylocker. unlock () called. 3 Before _ deco called. Mylocker. acquire () called. Before myfunc2 called. Lockerex. acquire () called. Myfunc2 () called. Lockerex. unlock () called. Mylocker. unlock () called. 7

I hope this article will help you with Python programming.