scalar vs array and program control

Sebastian P. Luque spluque at gmail.com
Sat Jul 25 17:30:58 CEST 2015


On Sat, 25 Jul 2015 14:44:43 +0200,
Laura Creighton <lac at openend.se> wrote:

> And because I was rushed and posted without revision I left out
> something important.

>> So this is, quite likely, the pattern that you are looking for:

>> try: all_your_code_which_is_happy_with_non_scalars except
>> WhateverErrorPythonGivesYouWhenYouTryThisWithScalars:
>> whatever_you_want_to_do_when_this_happens

>> This is the usual way to do things.

> I forgot to tell you that you are supposed to stick the try/except
> around the smallest chunk of code that you expect to get the
> exception.

> So you write this as

> code_you_expect_always_to_work more_code_you_expect_always_to_work

> try: these_four_lines_of_code_that_will_be_unhappy_if_its_a_scalar
> except ValueError: # whatever kind of error the real error is
> whatever_you_want_to_do_when_that_happens

> The reason is that if you get any Value Errors in the part of the code
> you always expect to work, then you don't want your program to run
> happily along running the code for 'its a scalar'.  You don't want to
> hide real errors here.

> The other thing I forgot to mention is that sometimes you don't want
> to do anything but ignore any errors of this sort.

> Thats written like this:

> code_you_expect_always_to_work more_code_you_expect_always_to_work

> try: these_four_lines_of_code_that_will_be_unhappy_if_its_a_scalar
> except ValueError: pass # just ignore it

Thanks so much for all the pointers, and especially how `try` is used in
practice.  Avoiding the tangle of checks for kind of input is precisely
what my intuition was telling me.


-- 
Seb



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