Extended List Comprehension

[James Stroud]

Would anyone else find this syntax useful for generator expressions?

py> [x for x in '1234' if x%2 else 'even']
[1, 'even', 3, 'even']

I'm guessing this has been suggested before?

James

[Paul Rubin]

Re: Extended List Comprehension

James Stroud <jstroud@ucla.e du> writes:[color=blue]
> py> [x for x in '1234' if x%2 else 'even']
> [1, 'even', 3, 'even']
>
> I'm guessing this has been suggested before?[/color]

You could (in 2.5) use:

[(x if x%2 else 'even') for x in '1234']

[James Stroud]

Re: Extended List Comprehension

James Stroud wrote:[color=blue]
> Would anyone else find this syntax useful for generator expressions?
>
> py> [x for x in '1234' if x%2 else 'even']
> [1, 'even', 3, 'even']
>
> I'm guessing this has been suggested before?
>
> James[/color]

Before anyone notices, I should say:

[x for x in [1,2,3,4] if x%2 else 'even']

Darn'ed imaginary interpreters!

[Tim Chase]

Re: Extended List Comprehension

>>py> [x for x in '1234' if x%2 else 'even'][color=blue][color=green]
>>[1, 'even', 3, 'even']
>>
>>I'm guessing this has been suggested before?[/color]
>
>
> You could (in 2.5) use:
>
> [(x if x%2 else 'even') for x in '1234'][/color]

This failed on multiple levels in 2.3.5 (the "if" syntax is
unrecognized, and trying the below with '1234' rather than
[1,2,3,4] choked) Haven't played with 2.5 yet, so this might be
a good way to go if you've got it.

However, this worked in my 2.3.5:

[((x%2 == 0 and 'even') or x) for x in [-2,-1,0,1,2,3,4]]

It uses the fairly defacto short-circuit-evaluation usage to coin
a Python trinary operator like the C/C++ colon/question-mark pair
of operators.

There is a caveat (that can be coded around, IIRC, but don't have
it at the tip of my fingers) that inverting the logic can cause
trouble when x==0 as in

[((x%2 == 0 and x) or 'odd') for x in [-2,-1,0,1,2,3,4]]

which doesn't quite produce the desired results.

-tim@justonemore tim.com

[Ido Yehieli]

Re: Extended List Comprehension

As Paul already demonstrated, this is hardly needed since it can be
done more clearly with existing lang. features.

[Joel Bender]

Re: Extended List Comprehension

> You could (in 2.5) use:[color=blue]
>
> [(x if x%2 else 'even') for x in '1234'][/color]

Or this:

[int(x)&1 and x or 'even' for x in '1234']

[Paul Rubin]

Re: Extended List Comprehension

Tim Chase <python.list@ti m.thechases.com > writes:[color=blue][color=green]
> > You could (in 2.5) use:
> > [(x if x%2 else 'even') for x in '1234'][/color]
>
> This failed on multiple levels in 2.3.5 (the "if" syntax is
> unrecognized,[/color]

Yes, that syntax is new to 2.5.
[color=blue]
> However, this worked in my 2.3.5:
> [((x%2 == 0 and 'even') or x) for x in [-2,-1,0,1,2,3,4]]
> It uses the fairly defacto short-circuit-evaluation usage to coin a
> Python trinary operator like the C/C++ colon/question-mark pair of
> operators.[/color]

Yeah, you could do that, but there's various drawbacks, hence the new
syntax being introduced in 2.5.