Add methods to a class dynamically

[Hoang Do]

I am having trouble invoking the created method.  The function addition goes
fine but invoking it gives an error.  Here is some simple code:
---------------------------------------------------------
class DynObj:
    def __init__(self):
        self.methods = ("a", "b", "c")
        for method in self.methods:
           self. __generateMethod(method)
    def __generateMethod(self, methodName):
        code = "def %s(self):\n\tprint %s\n" % (methodName, methodName)
        exec code in globals(), self.__dict__

if __name__ == "__main__":
    x = DynObj()
    print dir(x)
    x.a(x)
---------------------------------------------------------
The Error:
NameError: global name 'a' is not defined
---------------------------------------------------------
Methods "a", "b", and "c" are callable and in DynObj's __dict__.  However, I
can't seem to call it.

Calling for help from anyone familiar with Python's introspective features?