[erlang-questions] lists:seq/[2,3] bug?

David Mercer <>
Thu Sep 18 17:07:32 CEST 2008


Zvi wrote:
> 2. I'm all about common sence, and behaviour we expect must be consistent
> with similar constructs in other languages from Basic to Matlab.
> Python's   "range([start,] stop [,step]) -> list of integers"  construct
> is
> not a good example, b/c "stop" isn't included (which is counter-intuitive)
> and it's also defined only on integers. See example at the end of the
> message.

I can't speak for Python, but I disagree that it is counterintuitive.  I
often expect ranges to include the lower bound but exclude the upper bound.
Granted, these are typically continuous ranges, such as dates: e.g., if I
want to query a database for all transaction for the week of September 1, I
specify the range from September 1 to September 1+7.  Since the range
excludes the upper bound, September 8, I have a correct specification.

If anything, I find including the upper bound counterintuitive.  Take any
arbitrary values of start, stop, and step: does the sequence include the
stop or not?  You can't know because it does when (stop - start) mod step ==
0, but otherwise it does not.  I'd say, to be consistent, we should exclude
the stop, but that probably really would break some people's code...

Cheers,

David




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