Feature or enhancement

Proposal:

It would be useful to be able to search a list in a functional-style manner. :

# list with structured data
data = [(i, chr(i)) for i in range(100)]

# find index of "a" in classic manner:
for idx, item in enumerate(data):
    if item[1] == "a":
        break

# functional-style search:
idx = data.index("a", key=lambda i: i[1])

This idea came up in the discussion to pr #112498, in the context of searching for objects in a heap.

Task = namedtuple('Task', ('priority', 'name', 'timestamp', 'callback'))
data: List[Task] = get_data()

# remove "bob"
del data[data.index("bob", key=attrgetter("name"))]

An implementation is provided in pr #113772

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

I mentioned this in pr #112498, as a way to decouple searching and heap removal.
Instead of having

heapq.heapremove(heap, value, key=keymethod)

the desired functionality could be easily provided if list itself provided the search functionality:

heapq.heapremove(heap, heap.index(value, key=keymethod))

Linked PRs

• gh-113773: add list.index() "key" named argument #113772