Dynamic/runtime method creation (code generation) in Python

Question

I need to generate code for a method at runtime. It\'s important to be able to run arbitrary code and have a docstring.

I came up with a solution combining exe

Answer 1

Python will let you declare a function in a function, so you don't have to do the exec trickery.

def __init__(self):

    def dynamo(self, arg):
        """ dynamo's a dynamic method!
        """
        self.weight += 1
        return arg * self.weight
    self.weight = 50

    setattr(self.__class__, 'dynamo', dynamo)

If you want to have several versions of the function, you can put all of this in a loop and vary what you name them in the setattr function:

def __init__(self):

    for i in range(0,10):

        def dynamo(self, arg, i=i):
            """ dynamo's a dynamic method!
            """
            self.weight += i
            return arg * self.weight

        setattr(self.__class__, 'dynamo_'+i, dynamo)
        self.weight = 50

(I know this isn't great code, but it gets the point across). As far as setting the docstring, I know that's possible but I'd have to look it up in the documentation.

Edit: You can set the docstring via dynamo.__doc__, so you could do something like this in your loop body:

dynamo.__doc__ = "Adds %s to the weight" % i

Another Edit: With help from @eliben and @bobince, the closure problem should be solved.