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+--- Thread: iterating and detecting the last (/thread-38347.html)
iterating and detecting the last - Skaperen - Sep-30-2022
i am iterating over a list (or tuple). for each item except the last item i need to do a specific thing. for the last item i need to do something different. the solution i am thinking about is to get the initial len() of the list and count as the iterating proceeds. if the counting is up, i detect the last when the count equals the length. another way is iterating over range(len(seq)-1) and indexing the sequence like:
for x in range(len(seq)-1):
foo(seq[x])
bar(seq[-1])there are many ways to do this. which would be the best? which would be most pythonic?
RE: iterating and detecting the last - Yoriz - Sep-30-2022
items = [1, 2, 3, 4]
for item in items[:-1]:
print(item)
print(f"last item = {items[-1]}")Output:1
2
3
last item = 4RE: iterating and detecting the last - bowlofred - Sep-30-2022
If you know it's a sequence (which list and tuples are), I'd just iterate over obj[:-1].
If it's something that isn't a sequence (like a generator), then you could just stick the current object in a cache and operate on it after you read the next item.
for element in seq[:-1]:
foo(element)
bar(seq[-1])or:i = iter(obj)
cache = next(i)
for item in i:
foo(cache)
cache = item
bar(cache)
RE: iterating and detecting the last - Gribouillis - Oct-01-2022
The cache strategy is also implemented in
more_itertools.peekable()for item in (p := peekable(iterable)):
if not p:
print(f"Item {item} is the last one")
else:
print("Not the last item")