which is more 'pythonic' / 'better' ?

[Steven Bethard]

Peter Hansen wrote:
> def meth(self, things=None):
>     self.things = things or []
> 
[snip]
> 
> The alternative is fine too, but insisting on it would be pedantic, and 
> if you have more than one of these it is definitely less readable (and, 
> therefore, not Pythonic):
> 
> def meth(self, things=None):
>     if things:
>         self.things = things
>     else:
>         self.things = []

Probably worth pointing out that there is at least one more alternative:

def meth(self, things=None):
     if things is None:
         things = []
     self.things = things

I usually opt for this one, mainly because "things or []" makes me 
nervous -- it has different behavior if the user passes in an empty list:

py> class Things1(object):
...     def __init__(self, things=None):
...         if things is None:
...             things = []
...         self.things = things
...
py> class Things2(object):
...     def __init__(self, things=None):
...         self.things = things or []
...
py> lst = []
py> thing = Things1(lst)
py> thing.things.append(100)
py> thing.things, lst
([100], [100])
py> lst = []
py> thing = Things2(lst)
py> thing.things.append(100)
py> thing.things, lst
([100], [])

That said, I do use "and" and "or" occasionally when I'm sure I don't 
have to worry about complications like the above.  I've probably even 
used them in an assignment statement. ;)

STeVe