Marc Aymerich wrote:
> Hi,
>
> I'm playing a bit with python dynamic methods and I came up with a
> scenario that I don't understant. Considering the follow code:
>
> # Declare a dummy class
> class A(object):
> pass
>
> # generate a dynamic method and insert it to A class
> for name in ['a', 'b', 'c']:
> if name == 'b':
> @property
> def get_name(self):
> return name
> A.name = get_name
>
>
> a_instance = A()
> a_instance.name
>
> # So far I exptect that a_instance.name returns 'b', since it has
> been created when name == 'b', but this is what actually returns:
>
>>>> a_instance.name
> 'c'
>
> just the last 'name' value.
> What can I do in order to generate a method like this but that returns
> 'b' ? What is wrong in my understanding of this pice of code?
Look at the method again:
> def get_name(self):
> return name
It returns the global variable name. Why would you expect to see a
historical value of that variable?
If you want to capture the value of name at the time when get_name() is
defined you have several options:
- The default argument trick:
def get_name(self, name=name):
return name
- A closure:
def make_get_name(name):
def get_name(self):
return name
return get_name
A.name = property(make_get_name(name))
- functools.partial()
def get_name(self, name):
return name
A.name = property(partial(get_name, name=name))
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