On Jul 13, 7:00 pm, Terry Reedy <[EMAIL PROTECTED]> wrote:
> Tim Cook wrote:
> > I guess I can classify my application(s) as more procedural than
> > anything else. But I have a question about the best way to handle
> > something in Python.
>
> > When given a mapping of keywords, I want to call a function based on a
> > certain keyword found when parsing a text file. The mapping looks like
> > this:
>
> > definClassMap={'SECTION':'bldSection','COMPOSITION':'bldComposition','OBSER
> > VATION':'bldObservation','ITEM_TREE':'bldItemTree'}
>
> > So if the text file contains 'ITEM_TREE' I want to call bldItemTree
> > which creates an instance of the class ItemTree.
>
> > I currently use an if ..., elif ... construct.
> > Is there a better, more efficient, more Pythonic way of doing this?
>
> Yes. Create a mapping of keywords to function objects rather than to
> function names!
>
> def bldSection(): <whatever>
> ...
> def bldItemTree(): <whatever else>
>
> class_map={
> 'SECTION':bldSection,
> 'COMPOSITION':bldComposition,
> 'OBSERVATION':bldObservation,
> 'ITEM_TREE':bldItemTree, # trailing comma allows easy additions
>
> }
>
> for word in parselist:
> try;
> class_map[word]()
> except KeyError:
> <whatever for non-keys>
A nice variant of this, which minimizes repetition, is to group all
the factory methods together into a class, naming them the same as the
keyword...
class Builder(object):
def SECTION(self):
...
def COMPOSITION(self):
...
def OBSERVATION(self):
...
def ITEM_TREE(self):
...
builder = Builder()
for word in parse_list:
item = getattr(builder, word)()
...
--
Paul Hankin
--
http://mail.python.org/mailman/listinfo/python-list
