...the range built-in in Python excludes the upper bound.
Makes sense from a mathematical point of view (combining different ranges is easier) but I prefer the more intuitive Perl way to do it.
Theoretically, I prefer semi-open ranges [begin, end), aka half-open intervals, because:
- The range size is simply "end - begin"
- Empty ranges are expressed as "begin equals end" and so do not require special handling
- Two subsequences are adjacent means that the upper bound of the one equals the lower bound of the other
This theoretical superiority was eloquently expressed in hand-written notes
by Edsger W Dijkstra in 1982, who further argued that
zero (not one) is the natural first array subscript,
as in [0, N). With typical attention to detail, I see that
the three page numbers of Dijkstra's note are: 0, 1, and 2! :)
In practice, I prefer Python semi-open ranges
to the inclusive (closed) ranges emitted by the Perl and Ruby range operator.
I remember finding Python's semi-open ranges nicer
when golfing with string slices.
After enjoying Python string slices, I miss them when coding in Perl;
the closest Perl equivalent, the substr function,
seems unwieldy by comparison.
Semi-open ranges also feel comfortable to me because they
form a crucial part of C++ STL, in particular iterators,
which in turn were influenced by C pointers and arrays.
Stepanov extended some common (semi-open) C idioms, such as:
for (i = 0; i < N; ++i) { // a[i] ... }
for (ptr = a; ptr < a+N; ++ptr)
inventing a more general iterator abstraction:
for (iter = begin; iter != end; ++iter)
thus enabling STL algorithms to work on any container
that implements the iterator interface.
References
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