Suggestion: make sequence and map interfaces more similar

[Steven D'Aprano]

On Thu, 31 Mar 2016 03:52 am, Random832 wrote:

> Like, these are common patterns:
> 
> for i, x in enumerate(l):
>    # do some stuff, sometimes assign l[i]
> 
> for k, v in d.items():
>    # do some stuff, sometimes assign d[k]


for a, b in zip(spam, eggs):
    # do some stuff, sometimes assign x[a] or b[a] or who knows what?


Does this mean that "lists, dicts and zip" should all support the same
interface?

Not every coincidental and trivial piece of similar code is actually
related.


> A way to apply that pattern generically to an object which may be either
> a sequence or a mapping might be nice.

Nice, and easy.

# Duck-typing version.
def iterpairs(obj):
    if hasattr(obj, 'items'):
        it = obj.items
    else:
        it = enum(obj)
    yield from it


# Type-checking version.
def iterpairs(obj):
    if isinstance(obj, collections.abc.Mapping):
        it = obj.items
    elif isinstance(obj, collections.abc.Sequence):
        it = enum(obj)
    else:
        raise TypeError('not a sequence or a mapping')
    yield from it


Pick which one you prefer, stick it in your own personal toolbox of useful
utilities functions, and off you go.




-- 
Steven