ternary operator
Alex Martelli
aleax at aleax.it
Fri Feb 7 18:05:46 CET 2003
<posted & mailed>
Andrew Koenig wrote:
> David> I think that's POOR programming practice!
>
> Then how would you write the following loop?
>
> i = 0;
> while i < len(n) and x[i] != y:
> i += 1
Hmmm, the fact that i<len(n) gives no guarantee that
i is a valid index on x, in general. So, I'm not sure
if you may not perchance mean i<len(x) instead, which
might be a more ordinary case.
If so, and x is a list, then:
i = x.index(y)
is, I think, the best approach in Python.
If x was (for example) a tuple, and/or assuming that n
is not necessarily x but may refer to another sequence
which is known to be no longer than x, then I might
code this as:
for i in range(len(n)):
if x[i] == y: break
or, in Python 2.3 -- if n is actually x, then:
for i, thingy in enumerate(x):
if thingy == y: break
or without the n <-> x identification, then:
for i, thingy in enumerate(x):
if i>=len(n) or thingy == y: break
None of this is meant to deny the usefulness of
the short-circuiting and/or operators. It's just
that there are several attractive alternatives for
this _specific_ case in Python, but of course many
other cases exist where relying on and/or short-
circuit semantics yields the most elegant solution.
Alex
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