[Python] Dynamic/runtime method creation (code generation) in Python

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 exec and setattr, here's a dummy example:

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

d = {}
exec code.strip() in d
setattr(self.__class__, 'dynamo', d['dynamo'])


if __name__ == "__main__":
v = Viking()
print v.dynamo(10)
print v.dynamo(10)
print v.dynamo.__doc__


Is there a better / safer / more idiomatic way of achieving the same result?

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