define_method_from_str.py

# Get some code that does something in a class. Note that the code is a string.
code="""

def to_string(self):
    print "x=", self.x

"""

# Print that code into a temporary Python module
with open("zzz.py","wt") as py:
    print >> py, code

# Now import that
from zzz import to_string

#What did we get?
print "to_string is:", to_string

#Can we actually smuggle this as a method into a class? Of course!

#Here's the victim:
class SomeObject:

    def __init__(self,x):
        self.x=x

#...and here we just add a method on the fly
SomeObject.to_string=to_string

#Make an object
o1=SomeObject(1)
#Lo and behold! It works!
o1.to_string()