Scope of lambda functions and their parameters?

Question

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.

Answer 1

The variable m is being captured, so your lambda expression always sees its "current" value.

If you need to effectively capture the value at a moment in time, write a function takes the value you want as a parameter, and returns a lambda expression. At that point, the lambda will capture the parameter's value, which won't change when you call the function multiple times:

def callback(msg):
    print msg

def createCallback(msg):
    return lambda: callback(msg)

#creating a list of function handles with an iterator
funcList=[]
for m in ('do', 're', 'mi'):
    funcList.append(createCallback(m))
for f in funcList:
    f()

Output:

do
re
mi