[Tutor] Fwd: File IO help
Kent Johnson
kent37 at tds.net
Fri Oct 28 15:44:01 CEST 2005
Liam Clarke wrote:
> And, a question for the group, I've always found that line[:1] is a
> complicated way of writing line[0]... is there any time when line[:1]
> != line[0]?
Actually I would say that the general case is for them to be different and in the special case where line is a string they are the same.
line[0] means, "the first element of the sequence line"
line[:1] means, "the sequence consisting of everything from the start of line up to (but not including) line[1]"
If line is a list, these two meanings are different:
>>> r=range(4)
>>> r
[0, 1, 2, 3]
>>> r[0]
0
>>> r[:1]
[0]
In the case of a string, line[0] is actually a sequence itself - a new string. This is kind of strange, really, that an element of a sequence can be the same as a subsequence of the sequence. It is a consequence of Python not having a character type - single characters are represented as strings.
Kent
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http://www.kentsjohnson.com
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