can list comprehensions replace map?

[Peter Otten]

Me:

Could make it one line shorter with

from itertools import chain, izip, repeat
def fillzip(*seqs):
def done_iter(done=[len(seqs)]):
done[0] -= 1
if not done[0]:
return []
return repeat(None)
seqs = [chain(seq, done_iter()) for seq in seqs]
return izip(*seqs)

Peter Otten:

that won't work because done_iter() is now no longer a generator.
In effect you just say

seqs = [chain(seq, repeat(None)) for seq in seqs[:-1]] + [chain(seq[-1],
[])]

It does work - I tested it. The trick is that izip takes iter()
of the terms passed into it. iter([]) -> an empty iterator and
iter(repeat(None)) -> the repeat(None) itself.

Seems my description didn't convince you. So here's an example:
.... def done_iter(done=[len(seqs)]):
.... done[0] -= 1
.... if not done[0]:
.... return []
.... return repeat(None)
.... seqs = [chain(seq, done_iter()) for seq in seqs]
.... return izip(*seqs)
....

list(fillzip(range(6), range(3))) [(0, 0), (1, 1), (2, 2)]

versus

[(0, 0), (1, 1), (2, 2), (3, None), (4, None), (5, None)]

Now where's the typo?

'Course then the name should be changed.

My variable names where ill-chosen to begin with.

Peter

 

[Peter Otten]

Can I play too?

Not unless you buy the expensive but good-looking c.l.py gaming license
which is only available trough me

How about:
import itertools

def fillzip(*seqs):
def Nones(countactive=[len(seqs)]):
countactive[0] -= 1
while countactive[0]:
yield None
seqs = [itertools.chain(seq, Nones()) for seq in seqs]
return itertools.izip(*seqs)

You may be introducing a lot of extra tests in the while loop with the
non-constant condition -- which in practice is fairly cheap, though.
I'm willing to take the performance hit for the introduction of sane
variable names alone...

Peter

 

[Andrew Dalke]

Seems my description didn't convince you. So here's an example:

Got it. In my test case the longest element happened to be the last
one, which is why it didn't catch the problem.

Thanks.

Andrew
(e-mail address removed)