I need a callback function that is almost exactly the same for a series of gui events. The function will behave slightly differently depending on which event has called it. Seems like a simple case to me, but I cannot figure out this weird behavior of lambda functions.

So I have the following simplified code below:

    def callback(msg):
    	print msg

    #creating a list of function handles with an iterator
    funcList=[]
    for m in (&#39;do&#39;, &#39;re&#39;, &#39;mi&#39;):
    	funcList.append(lambda: callback(m))
    for f in funcList:
    	f()

    #create one at a time
    funcList=[]
    funcList.append(lambda: callback(&#39;do&#39;))
    funcList.append(lambda: callback(&#39;re&#39;))
    funcList.append(lambda: callback(&#39;mi&#39;))
    for f in funcList:
    	f()

The output of this code is:

    mi
    mi
    mi
    do
    re
    mi

I expected:

    do
    re
    mi
    do
    re
    mi

Why has using an iterator messed things up?

I&#39;ve tried using a deepcopy:

    import copy
    funcList=[]
    for m in (&#39;do&#39;, &#39;re&#39;, &#39;mi&#39;):
    	funcList.append(lambda: callback(copy.deepcopy(m)))
    for f in funcList:
    	f()

But this has the same problem.


Scope of lambda functions and their parameters?

I was reading about closures on the net. I was wondering if C++ has a built-in facility for closures or if there is any way we can implement closures in C++?


All Lexical Closures Solutions on Gang of Coders

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Scope of lambda functions and their parameters?

Do we have closures in C++?