can list comprehensions replace map?

[Peter Otten]

Andrew Dalke wrote:

> 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:

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

versus

>>> map(None, range(6), range(3))
[(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