Steven D'Aprano wrote:
> Sometimes people look for a method which is equivalent to dict.get, where
> they can set a default value for when the key isn't found:
>
>
> py> d = {1: 'a', 2: 'b'}
> py> d.get(999, '?')
> '?'
>
>
> The equivalent for sequences such as lists and tuples is a slice. If the
> slice is out of range, Python returns a empty sequence:
>
> py> L = [2, 4, 8, 16]
> py> L[5] # out of range, raises IndexError
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> IndexError: list index out of range
> py> L[5:6] # out of range slice return empty list
> []
>
> To get a default:
>
> py> L[5:6] or -1
> -1
>
>
> This is short and simple enough to use in place, but we can also wrap this
> into a convenient helper function:
>
> def get(seq, index, default=None):
> return (seq[index:index+1] or [default])[0]
>
>
>
> py> get(L, 2, -1)
> 8
> py> get(L, 200, -1)
> -1
But note:
>>> def get(seq, index, default=None):
... return (seq[index:index+1] or [default])[0]
...
>>> get("abc", -1, "default")
'default'
God old try...except to the rescue:
>>> def get(seq, index, default=None):
... try: return seq[index]
... except IndexError: return default
...
>>> get("abc", -1, "default")
'c'
--
https://mail.python.org/mailman/listinfo/python-list
