Dave,
Thanks for enlightening me and providing a solution.
I am a recent Python convert (from Perl). Hence the confusion about
generators.(Coroutines are not a standard part of Perl anyway)
- Joe
Dave Angel wrote:
Joe Python wrote:
I have a generator as follows to do list calculations.
*result = [(ListA[i] - ListB[i-1])/ListA[i] for i in range(len(ListA))]*
The above generator, throws '*ZeroDivisionError*' exception if
ListA[i] =
0.
Is there a way to say 'Don't divide by ListA[i] if its equal to 0
(within
that statement)'.
Sorry if this question sounds too stupid.
TIA
Joe
Doesn't sound stupid to me at all.
Short answer is a conditional expression. Replace
(ListA[i] - ListB[i-1])/ListA[i]
with
(ListA[i] - ListB[i-1])/ListA[i] if ListA[i] else 1.0
and you'll see 1.0 whenever ListA[i] == 0, and your original value
otherwise.
But I see a couple of other things. You're calling this a generator
when it's a list comprehension. For short lists, that frequently
doesn't matter, but in case it does, you could start by replacing the
braces on the outside with parentheses.
Next question is the two lists are the same length. And final one is
whether you really meant the offset of one when accessing ListB. If
the lists are both of length 4, you're doing something like
(a0 - b3)/a0 (a1-b0)/a1 (a2-b1)/a2 (a3-b2)/a3
In other words, you're using the last item of ListB for the first
division.
If that's really what you want, consider the following generator:
gen = ((a-b)/a if a!=0.0 else 1.0 for a,b in zip(ListA,
ListB[-1:]+ListB))
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