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 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?

Answer 1

Based on Theran’s code, but extending it to methods on classes:

   class Dynamo(object):     pass  def add_dynamo(cls,i):     def innerdynamo(self):         print 'in dynamo %d' % i     innerdynamo.__doc__ = 'docstring for dynamo%d' % i     innerdynamo.__name__ = 'dynamo%d' % i     setattr(cls,innerdynamo.__name__,innerdynamo)  for i in range(2):     add_dynamo(Dynamo, i)  d=Dynamo() d.dynamo0() d.dynamo1()   

Which should print:

  in dynamo 0 in dynamo 1