python的闭包和装饰器

概述closurehttps://www.programiz.com/python-programming/closuredefget_config_table():cfg={'a':1,'b':2}returncfgdefget_config_index():config_table=get_config_table()defwrapper(cfg_name):returnconfi closure

https://www.programiz.com/python-programming/closure

def get_config_table():    cfg = {'a':1, 'b':2}    return cfgdef get_config_index():    config_table = get_config_table()    def wrapper(cfg_name):        return config_table.get(cfg_name, 'NulL')    return wrapper

f=get_config_index()

f('a')

1

decoratordecorator pattern

Simple demo

from datetime import datetimefrom functools import wrapsdef time_this(func):    #@wraps(func)    def wrapper(*args, **kwargs):        begin = datetime.Now()        res = func(*args, **kwargs)        end = datetime.Now()        print("{} costs:{}".format(func.__name__, end - begin))        return res    return wrapper@time_thisdef count(num):    import time    time.sleep(num)def count1(num):    import time    time.sleep(num)count1 = time_this(count1)count(2)count1(2)class Foo:    @time_this    def _sub(self, n):        print("_sub")    @time_this    def foo1(self, num):        self._sub(9)        print("Foo.foo1")f = Foo()f.foo1(2)

count costs:0:00:02.000687count1 costs:0:00:02.000561_sub_sub costs:0:00:00.000988Foo.foo1foo1 costs:0:00:00.000988

discussion

decorating happens durning import

understand it by count = time_this(count), syntactic suger make it easy to use but far to understand

cellphone case

make a cellphone

make cellphone wrapper

wrap—>return a closure which stores the function

a case of closure

With parameterdefine

from functools import wrapsdef requires_permission(sPermission):                                def decorator(fn):        @wraps(fn)        def decorated(*args,**kwargs):                   print("by function decorator")            lPermissions = get_permissions(current_user_ID())                 if sPermission in lPermissions:                                       return fn(*args,**kwargs)                                     raise Exception("You need '{}' permission".format(sPermission))                          return decorated                                              return decorator       def get_permissions(iUserID):    return {1: ('logged_in', 'premium_member')}[iUserID]                         @requires_permission('administrator')def delete_user(iUserID):    pass@requires_permission('logged_in')def new_game():    pass@requires_permission('premium_member')def premium_checkpoint():    passdef current_user_ID():    return 1

Test

def test():    from functools import partial    for fun in (partial(delete_user, 1), new_game, premium_checkpoint):        try:            fun()        except Exception as e:            print("test {} with error '{}'".format(fun, str(e)))        else:            print("test {} OK".format(fun))test()

test functools.partial(<function require_permission_by_class_v1.__call__.<locals>.wrapper at 0x00000215357198B8>, 1) with error 'permission denIEd'test <__main__.require_permission_by_class object at 0x0000021534BA32C8> OKtest <__main__.require_permission_by_class object at 0x0000021534BA3FC8> OK

Decorator as class

class require_permission_by_class(object):    def __init__(self, permission, func):        self._func = func        self._permission = permission    def __call__(self, *args, **kwargs):        print("by class for {}".format(self._func.__name__))        lPermissions = get_permissions(current_user_ID())             if self._permission in lPermissions:                                   return self._func(*args,**kwargs)                                 raise Exception("permission denIEd")        def get_permissions(iUserID):    return {1: ('logged_in', 'premium_member')}[iUserID]                         def delete_user(iUserID):    passdelete_user=require_permission_by_class('administrator', delete_user)def new_game():    passnew_game=require_permission_by_class('logged_in', new_game)dec1=lambda f:require_permission_by_class('premium_member', f)@dec1def premium_checkpoint():    pass#premium_checkpoint=require_permission_by_class('premium_member', premium_checkpoint)def current_user_ID():    return 1def test():    from functools import partial    for fun in (partial(delete_user, 1), new_game, premium_checkpoint):        try:            fun()        except Exception as e:            print("test {} with error '{}'".format(fun, str(e)))        else:            print("test {} OK".format(fun))test()

by class for delete_usertest functools.partial(<__main__.require_permission_by_class object at 0x0000021534C20348>, 1) with error 'permission denIEd'by class for new_gametest <__main__.require_permission_by_class object at 0x0000021535441948> OKby class for premium_checkpointtest <__main__.require_permission_by_class object at 0x0000021534D18C08> OK

Another way

class require_permission_by_class_v1(object):    def __init__(self, permission):        self._permission = permission    def __call__(self, func, *args, **kwargs):        def wrapper(*args, **kwargs):            print("by class v1 for {}".format(func.__name__))            lPermissions = get_permissions(current_user_ID())                 if self._permission in lPermissions:                                       return self._func(*args,**kwargs)            raise Exception("permission denIEd")        return wrapper@require_permission_by_class_v1('administrator')def delete_user(iUserID):    pass#delete_user=require_permission_by_class_v1('administrator')(delete_user)

Test

test()

by class v1 for delete_usertest functools.partial(<function require_permission_by_class_v1.__call__.<locals>.wrapper at 0x0000021534F9FCA8>, 1) with error 'permission denIEd'by class for new_gametest <__main__.require_permission_by_class object at 0x0000021535441948> OKby class for premium_checkpointtest <__main__.require_permission_by_class object at 0x0000021534D18C08> OK

decorate multiple times

def retry(nums):    def decorator(fun):        def wrapper(*args, **kwargs):            for i in range(nums):                try:                    return fun(*args, **kwargs)                except Exception as e:                    print("{} fail{}".format(fun.__name__, ' retry...' if i < nums -1 else ''))        return wrapper    return decorator@time_this@retry(3)def must_be_fail():    raise Exception("bad guy")must_be_fail()

SummaryAdd aditional function before and after functionKNow the classic usage cases to give you enlightenment: logtime costexception handlepermission managerretry…

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