Re: Functional/Best?

[Terry Reedy]

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','OBSERVATION':'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>

tjr

[Paul Hankin]

On Jul 13, 7:00*pm, Terry Reedy <[e-mail]:

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