Avoiding if..elsif statements

[unexpected]

I have a program where based on a specific value from a dictionary, I
call a different function. Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?

Code:

value = self.dictionary .get(keyword)[0]

if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()

Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?

[Fredrik Lundh]

Re: Avoiding if..elsif statements

"unexpected " <sumesh.chopra@ gmail.comwrote:

I have a program where based on a specific value from a dictionary, I
call a different function. Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?
>
Code:
>
value = self.dictionary .get(keyword)[0]
>
if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()
>
Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?

but of course (did you try it?). here's an outline:

dispatch = {
"something" : somethingClass. func, # note: no () here
"somethingElse" : somethingElseCl ass.func,
"anotherthi ng": anotherthingCla ss.func,
"yetanotherthin g": yetanotherthing Class.func,
}

...

dispatch[value]() # note: do the call here!

or, a bit more robust:

try:
func = dispatch[value]
except KeyError:
print "- no handler for", value
else:
func()

tweak as necessary.

</F>

[Daniel Nogradi]

Re: Avoiding if..elsif statements

Code:

>
value = self.dictionary .get(keyword)[0]
>
if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()
>
Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?

How about (untested):

def x():
print 'x'

def y():
print 'y'

funcdict={ 'valuex': x, 'valuey': y }

funcdict['valuex']()

[Simon Forman]

Re: Avoiding if..elsif statements

unexpected wrote:

I have a program where based on a specific value from a dictionary, I
call a different function. Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?
>
Code:
>
value = self.dictionary .get(keyword)[0]
>
if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()
>
Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?

Yup.

dispatch = dict(
something = somethingClass. func,
somethingElse = somethingElseCl ass.func,
anotherthing = anotherthingCla ss.func,
yetanotherthing = yetanotherthing Class.func
)

def default():
pass


# call it like this

dispatch.get(sw itch_value, default)()

[Chaz Ginger]

Re: Avoiding if..elsif statements

unexpected wrote:

I have a program where based on a specific value from a dictionary, I
call a different function. Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?
>
Code:
>
value = self.dictionary .get(keyword)[0]
>
if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()
>
Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?
>

Why not do it this way?

foo =
{'something':so methingClass.fu nc,'somethingel se':somethingel seClass.func)

if foo.has_key(val ue) :
foo[value]()
else :
raise OMG, "%s isn't known" % value

[unexpected]

Re: Avoiding if..elsif statements

the missing () was the trick!

However, I'm passing in a few variables, so I can't just take it
out-though every single function would be passing the same variables.

so something.func( ) is actually
something.func( string, list)

How would I modify it to include them? Sorry I didn't include them the
first time, I was trying to simplify it to make it easier...oops!

Fredrik Lundh wrote:

"unexpected " <sumesh.chopra@ gmail.comwrote:
>

I have a program where based on a specific value from a dictionary, I
call a different function. Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?

Code:

value = self.dictionary .get(keyword)[0]

if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()

Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?

>
but of course (did you try it?). here's an outline:
>
dispatch = {
"something" : somethingClass. func, # note: no () here
"somethingElse" : somethingElseCl ass.func,
"anotherthi ng": anotherthingCla ss.func,
"yetanotherthin g": yetanotherthing Class.func,
}
>
...
>
dispatch[value]() # note: do the call here!
>
or, a bit more robust:
>
try:
func = dispatch[value]
except KeyError:
print "- no handler for", value
else:
func()
>
tweak as necessary.
>
</F>

[Fredrik Lundh]

Re: Avoiding if..elsif statements

"unexpected " <sumesh.chopra@ gmail.comwrote:

However, I'm passing in a few variables, so I can't just take it
out-though every single function would be passing the same variables.
>
so something.func( ) is actually
something.func( string, list)
>
How would I modify it to include them?

just add the parameters to the call:

dispatch[value](string, list) # note: do the call here!

in Python, an explicit call is always written as

expression(argu ment list)

where expression yields a callable object. in your original case,
the expression was a bound method; in the modified example,
the expression is a dictionary lookup. the actual call part looks
the same way, in both cases.

</F>

[Carl Banks]

Re: Avoiding if..elsif statements

unexpected wrote:

Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?

Use something other than Perl.

:)


Carl Banks

[Ghalib Suleiman]

Re: Avoiding if..elsif statements

Try it and see. Functions are first-class citizens in Python.

On Aug 25, 2006, at 6:36 PM, unexpected wrote:

I have a program where based on a specific value from a dictionary, I
call a different function. Currently, I've implemented a bunch of
if..elsif statements to do this, but it's gotten to be over 30 right
now and has gotten rather tedious. Is there a more efficient way to do
this?
>
Code:
>
value = self.dictionary .get(keyword)[0]
>
if value == "something" :
somethingClass. func()
elsif value == "somethingElse" :
somethingElseCl ass.func()
elsif value == "anotherthi ng":
anotherthingCla ss.func()
elsif value == "yetanotherthin g":
yetanotherthing Class.func()
>
Is it possible to store these function calls in a dictionary so that I
could just call the dictionary value?
>
--
http://mail.python.org/mailman/listinfo/python-list

[Tal Einat]

Re: Avoiding if..elsif statements


Fredrik Lundh wrote:

"unexpected " <sumesh.chopra@ gmail.comwrote:
>

However, I'm passing in a few variables, so I can't just take it
out-though every single function would be passing the same variables.

so something.func( ) is actually
something.func( string, list)

How would I modify it to include them?

>
just add the parameters to the call:
>
dispatch[value](string, list) # note: do the call here!
>

This will work great if all of your functions recieve the same
argument(s). If not, there are still simple solutions.

I would suggest a solution like this, since it's simple and generic:

class Command (object):
def __init__(self, func, *args, **kw):
self.func = func
self.args = args
self.kw = kw
def __call__(self, *args, **kw):
args = self.args+args
kw.update(self. kw)
apply(self.func , args, kw)

An instance of the Command class can be called just like a function,
and it will call the orginial function with the arguments it was
instantiated with. (You can also pass additional arguments at the call
itself)

dispatch = {
"something" : Command(somethi ngClass.func),
"somethingElse" : Command(somethi ngElseClass.fun c, "moo",
[1,2,3]),
"anotherthi ng": Command(another thingClass.func , 'a', 'b', 'c'),
"yetanotherthin g": Command(yetanot herthingClass.f unc,
verbose=True),
}

dispatch[value]()

- Tal Einat
reduce(lambda m,x:[m[i]+s[-1] for i,s in enumerate(sorte d(m))],
[[chr(154-ord(c)) for c in '.&-&,l.Z95193+1 79-']]*18)[3]

[Fredrik Lundh]

Re: Avoiding if..elsif statements

Tal Einat wrote:

This will work great if all of your functions recieve the same
argument(s).

I assumed "every single function would be passing the same variables"
meant exactly that, of course.

</F>

[Tal Einat]

Re: Avoiding if..elsif statements


Fredrik Lundh wrote:

Tal Einat wrote:
>

This will work great if all of your functions recieve the same
argument(s).

>
I assumed "every single function would be passing the same variables"
meant exactly that, of course.
>
</F>

Right, as usual. I sort of missed that... ;)

- Tal