Hey all,
Often I've found this kind of code:
seen = set()
for i in iterable:
if i in seen:
... # do something in case of duplicates
else:
seen.add(i)
... # do something in case of first visit
This kind of code appears whenever one needs to check for duplicates in
case of a user-submitted iterable, or when we loop over a recursive
iteration that may involve cycles (graph search or the like). This code
could be improved if one could ensure an item is in the set, and get
whether it was there before in one operation. This may seem overly
specific, but dicts do do this:
seen = {}
for i in iterable:
if seen.set_default(i, some_value) is not None:
... # do something in case of duplicates
else:
... # do something in case of first visit
I think the set type would benefit greatly from its add method having a
return value. set.add would return True if the item was already in the set
prior to insertion, and False otherwise.
Looking at the Cpython code, the set_add_entry already detects existing
entries, adding a return value would require no additional complexity.
Any thoughts?
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