[Baypiggies] bound and unbound methods

Simeon Franklin simeonf at gmail.com
Sun Jun 24 07:49:07 CEST 2012

What version of Python are you using? The code below does work exactly
for me (2.6.5 on my unbuntu box) - but it isn't really illustrating
your question either. You have at class definition an existing class
method aliased to a new name (the "meth_cell = meth" line). But "meth"
will be a bound method of any instantiated objects and generally if
you add regular old functions dynamically to your classes Python
converts them to bound methods when making objects out of your class.
As long as your function takes a first parameter representing self
you're OK. So given your class I did

>>> k = K()
>>> k.another('asdf')

Everything seems to work. As to your question: If you have a function
defined outside the class you can add it to the class later with

>>> K.another_method = some_func

and things will just work. If you want to add functions to objects,
however, that's when things get tricky.
>>> def foo(self):
...     print self
>>> k = K()
>>> k.foo = foo
>>> k.foo()
TypeError: foo() takes exactly 1 argument (0 given)
>>> k.foo
<function foo at 0x...>

To attach a function to an object and convert it to a bound method
import types and convert it manually to a bound method

>>> k.foo = types.MethodType(foo, k, K)
>>> k.foo
<bound method K.foo of <__main__.K object at 0x989216c>>

Simeon Franklin

On Fri, Jun 22, 2012 at 10:53 PM, Ian Zimmerman <itz at buug.org> wrote:
> Is there any semi-clean way to transform an unbound method into a bound
> one?
> class K(object):
>      def meth(self, junk):
>          print junk
>      meth_cell = meth
>      def another(self, gunk):
>          # this doesn't work, what does?
>          self.meth_cell(gunk)
> --
> Ian Zimmerman
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