any such thing as list interleaving?

Re: any such thing as list interleaving?

Tom Plunket wrote:
[color=blue]
> I find myself often doing the following sort of thing (sorry for
> lack of whitespace, I don't want the line to break):
>
> for entry, index in map(lambda e,i:(e,i),aList ,range(len(aLis t)):
> # ...[/color]

In Python 2.3, you can write

for index, entry in enumerate(L):
# ...

For 2.2, you can define enumerate yourself:

def enumerate(L):
i = 0
while 1:
try:
yield i, L[i]
except IndexError:
return
i += 1

For older versions, yet another definition would be needed;
I leave that as an exercise.
[color=blue]
> This also brings up a similar problem for me when iterating over
> dictionaries:
>
> for key in myDict:
> value = myDict[key]
> # ...
>
> This seems a pretty sloppy way to go about it, imo. There must
> be something more in the Python spirit! :)[/color]

Here, you could always write

for key, value in myDict.items():
#...

Since 2.2, there is another method available which does not create
a list of tuples:

for key, value in myDict.iteritem s():
#...

HTH,
Martin

Re: any such thing as list interleaving?

On Sat, 12 Jul 2003 14:00:49 -0700, Tom Plunket <[email protected] g>
wrote:
[color=blue]
>
>I find myself often doing the following sort of thing (sorry for
>lack of whitespace, I don't want the line to break):
>
>for entry, index in map(lambda e,i:(e,i),aList ,range(len(aLis t)):
> # ...
>
>This definitely seems like a roundabout way to loop through
>parallel lists together. Is this map routine truly the easiest/
>best/most straight-forward way to do a for loop through parallel
>lists, if I feel that the Python anti-idom of:
>[/color]

Check the zip builtin:
[color=blue][color=green][color=darkred]
>>> help(zip)[/color][/color][/color]
Help on built-in function zip:

zip(...)
zip(seq1 [, seq2 [...]]) -> [(seq1[0], seq2[0] ...), (...)]

Return a list of tuples, where each tuple contains the i-th
element
from each of the argument sequences. The returned list is
truncated
in length to the length of the shortest argument sequence.

[color=blue]
>for index in range(len(myLis t)):
> entry = aList(index)
> anotherEntry = anotherList(ind ex)
> # ...
>
>???
>
>This also brings up a similar problem for me when iterating over
>dictionaries :
>
>for key in myDict:
> value = myDict[key]
> # ...
>[/color]

Fire the interpreter and type:
[color=blue][color=green][color=darkred]
>>> help(dict)[/color][/color][/color]

As it's a long stretch of text, I'll just post the relevant part:

| iteritems(...)
| D.iteritems() -> an iterator over the (key, value) items of D
|
[color=blue]
>This seems a pretty sloppy way to go about it, imo. There must
>be something more in the Python spirit! :)
>
>Thanks.
>
>-tom![/color]

With my best regards,
G. Rodrigues