Steven D'Aprano wrote:
> On Fri, Dec 27, 2019 at 02:22:48AM -0000, Marco Sulla via Python-ideas wrote:
> > It's very common to see:
> > for i, x in enumerate(sequence):
> > [...]
> >
> > Yes, that is very common, except that "sequence" can be any iterable
> with an unpredictable length, or even an infinite length, such as a
> generator
There's no problem. Also iterators and generators can have a entries() method
that returns a view, or a generator.
> that will cause a lot of code duplication. Just in the
> built-ins, we would have to add those two methods to:
>
> dicts
> dict views (keys, values and items)
> sets
> frozensets
> lists
> tuples
> strings
> bytes
> bytearrays
>
> (did I miss any?)
Yes and no: you added too much! dict views, set and frozenset are not
sequences, and furthermore does not require such methods. You missed
memoryview. About maps, well... wait and read ^^
And even if they are not sequences, I think also file-like objects can benefit
from an entries() method:
```
with open(somepath) as f:
for i, line in f.entries():
[...]
```
>. Even if the methods can share an implementation
> (probably calling enumerate and range behind the scenes)
This can be a fast and furious implementation for a first draft, but IMHO they
should return a view, like for maps.
> for i, x in enumerate(items): # works with every iterable
> for i, x in items.entries(): # only works with some sequences
Well, enumerate does work with **almost** every iterable. It does not work with
maps, you have to use keys(). You can say <<you can still use enumerate with a
map>>, but for another purpose.
Currently, if you want to iterate over a map items or over a sequence,
iterable, generator and file entries, you already have to use two different
APIs.
Maybe we can simply add an alias for keys() and entries() for maps, so we have
really them for all iterables.
Furthermore, there's also an unexpected bonus for enumerate: enumerate could
try to return entries() for not maps as first action. I don't know if enumerate
is written in py or in c, but if it's written in py, this will be boost
enumerate.
IMHO, indexes() could be simply added to all sequences without problems.
entries(), since it can be applied to not sequences too, IMHO requires another
CPython type: Enumerable. Who inherits also Enumerable must implement an
entries() method. This could be also an ABC class.
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