如何使用Python中的回调函数？ [英] How to use a callback function in python?
问题描述
我不知道如何正确使用Python 2.7回调函数。
I wonder how to correctly use python 2.7 callback functions.
我有权威性的CherryPy例子一些回调函数在我的code。
I have some callback functions from Cherrypy auth examples in my code.
（这些回调返回一个取值为真或假的函数，根据登录的用户组或不存在。）
(These callbacks return a function that can evaluate to True or False, depending on the logged in user being in a group or not.)
我不知道是否被执行或不回调，如果我写了一张code像这样的：
I wonder if a callback is executed or not if I write a piece of code like this:
由于从库中的定义是：
def member_of(groupname):
def check():
if groupname == 'admin':
if cherrypy.request.login == 'joe':
return True
if cherrypy.request.login == 'toni':
return True
return False
return False
# .... (other groups checked in the same way)
return check # returns a callback function from my understanding?
如何申请，在我的code执行回调？
How can I apply and execute the callback in my code?
如果我把它放在这样的：
If I put it like this:
if member_of('admin'):
do_something()
else:
do_something_else()
这是否会执行calllback并检查管理组？还是会发现，如果MEMBER_OF的值是一个函数的定义和函数定义大概是总是一个真值（或者以假值），但两者都是错误的，因为它需要执行
Will this execute the calllback and check for the admin group? Or will it find out if the value of "member_of" is a function definition and a function definition is probably always a "True" value (or maybe a False value) but both are wrong, because it needs to be executed
您可以告诉我这个？我怎样才能确保执行的回调？一个我怎么可以通过它周围，因为它是？
Can you enlighten me on this? How can I make sure a callback is executed? An how can I pass it around as it is?
推荐答案
在蟒蛇，就像许多其他语言，变量还可以包含一个功能，你可以通过他们周围像包含如其他变量数字或字符串。
In python, like in many other languages, a variable can also contain a function and you can pass them around like other variables that contain e.g. numbers or strings.
CherryPy的 MEMBER_OF 函数本身做你的榜样返回的功能。
CherryPy's member_of function itself does return a function in your example.
我解释它在简单的步骤：
I am explaining it in simple steps:
如果你写 MEMBER_OF（）返回）功能MEMBER_OF（的结果是一个名为检查在这种情况下。
If you write member_of() it returns the result of the function member_of() which is the function with the name check in this case.
cb_function = member_of('admin')
此时变量 cb_function 保存调用函数 MEMBER_OF 的结果，并在最后一行 MEMBER_OF 收益检查，这是在函数中定义的 MEMBER_OF 作为另一个功能！
At this point the variable cb_function holds the result of calling the function member_of, and in the last line member_of returns check, which was defined within the function member_of as another function!
您必须再次拨打第一个结果，因为你可以，你必须在几乎相同的方式把它当作一个局部的功能，那你在目前情况下的定义，得到最终的结果是，通过做类似：
You have to call the first result again, because you can and you have to treat it in almost the same way as a local function, that you defined in the current context, to get the final result, by doing something like:
my_result = cb_function()
然后你会继续并使用结果。例如，你可以检查它的布尔值：
And then you would continue and use the result. For example you could check its boolean value:
if my_result:
# do something
...
从上面在一起的3个步骤可以写成短：
The 3 steps from above together can be written shorter:
cb_function = member_of('admin')
if cb_function():
# do something
...
或者更短：
if member_of('admin')():
# do something
...
起初，它可能会出现一个有些奇怪的蟒蛇有双（）（），但如果你想想看一会儿它是有道理的。
At first it may appear a little strange in python to have the double ()(), but if you think about it for a while it makes sense.
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