On Fri, 30 Sep 2005 09:38:25 -0700, Michael Spencer <[EMAIL PROTECTED]> wrote:
>Terry Reedy wrote:
>> "David Murmann" <[EMAIL PROTECTED]> wrote in message
>> news:[EMAIL PROTECTED]
>>
>>>>def join(sep, seq):
>>>> return reduce(lambda x, y: x + sep + y, seq, type(sep)())
>>>
>>>damn, i wanted too much. Proper implementation:
>>>
>>>def join(sep, seq):
>>> if len(seq):
>>> return reduce(lambda x, y: x + sep + y, seq)
>>> return type(sep)()
>>>
>>>but still short enough
>>
>>
>> For general use, this is both too general and not general enough.
>>
>> If len(seq) exists then seq is probably reiterable, in which case it may be
>> possible to determine the output length and preallocate to make the process
>> O(n) instead of O(n**2). I believe str.join does this. A user written
>> join for lists could also. A tuple function could make a list first and
>> then tuple(it) at the end.
>>
>> If seq is a general (non-empty) iterable, len(seq) may raise an exception
>> even though the reduce would work fine.
>>
>> Terry J. Reedy
>>
>>
>>
>For the general iterable case, you could have something like this:
>
> >>> def interleave(sep, iterable):
> ... it = iter(iterable)
> ... next = it.next()
> ... try:
> ... while 1:
> ... item = next
> ... next = it.next()
> ... yield item
> ... yield sep
> ... except StopIteration:
> ... yield item
> ...
> >>> list(interleave(100,range(10)))
> [0, 100, 1, 100, 2, 100, 3, 100, 4, 100, 5, 100, 6, 100, 7, 100, 8, 100, 9]
> >>>
>
>but I can't think of a use for it ;-)
I have this version:
def interlace(x, i):
"""interlace(x, i) -> i0, x, i1, x, ..., x, iN
"""
i = iter(i)
try:
yield i.next()
except StopIteration:
return
for e in i:
yield x
yield e
And I use it for things like interleave(", ", ["foo", bar, "baz"]), where bar
is not a string, but can be handled along with strings by a lower-level chunk
of code.
Jp
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