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 ;-) Michael -- http://mail.python.org/mailman/listinfo/python-list
