[Python-ideas] get() method for list and tuples

[Michel Desmoulin]

Le 01/03/2017 à 01:02, Steven D'Aprano a écrit :
> On Tue, Feb 28, 2017 at 07:10:15PM +0100, Sven R. Kunze wrote:
> 
>> 1. advantage: it looks like dict access -> allows duck typing (oh how 
>> often I'd missed that)
> 
> Dicts and lists don't duck-type because they are very different things.
> 
> We know what ["item"]*10 does. What would {"key": "value"}*10 do?
> 
> What would list.values() iterate over?
> 
> 

The fact the API is not exactly the same doesn't prevent duck typing.
Duck typing is precesily about incomplete but good enough similar API.

For the dict and list:

- you can iterate on both
- you can index both
- you can size both

Hence I can see very well functions working with both. E.G: helper to
extract x elements or a default value:

def extract(data, *args, default="None"):
    for x in args:
        try:
            yield data[x]
        except (KeyError, ValueError):
            yield default

Usage:


a, b, c = extract(scores, "foo", "bar", "doh")
x, y, z = extract(items, 2, 5, 8, default=0)

I actually have this helper function.

With list.get and tuple.get, this would become:

def extract(data, *args, default="None"):
    return (data.get(x, default) for x in args)