On Apr 11, 2020, at 08:22, Eric Fahlgren <[email protected]> wrote:
>
>> On Sat, Apr 11, 2020 at 4:21 AM Rhodri James <[email protected]> wrote:
>> Since the introduction of enumerate() lo! these many moons ago, I find I
>> almost never write range(len(x)) as a loop iterable.
>
> Out of curiosity, I just grepped about 300k lines of source:
>
> 234 - enumerate() in for loops
> 140 - zip() in for loops
> 12 - range(len()) in for loops
>
> About half of those 12 range uses are interfacing to extension modules that
> only provide an indexing interface to array-like data, so really no way
> around it...
Actually, there is usually a way around it: just use enumerate/zip/etc. anyway.
Any type for which sq_item/__getitem__ raises IndexError on the len-th index
automatically is iterable, unless it goes out of its way to not be by
implementing a tp_iter/__iter__ that raises, or does something pathological.
And there are a few extension modules that explicitly implement a raising
tp_iter, usually by mistake, but most don’t.
In fact, this works even more generally than looping over range(len(x)). You
don’t even have to provide tp_len/__len__ (e.g., because you’re presenting a
dynamic Spam* array terminated by a sentinel value), and iteration still works.
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