CODEWITHSUNDEEP
pythonlist
Arash Hatami
Arash Hatami

Reputation: 5551

Python append to list or ignore

I want make an array as follow :

for i in range(0, len(final), 3):
    ar.append(
        (
            final[i] + 100,
            final[i+1] + 100,
            final[i+2] + 100
        )
    )

but there is a simple problem. length of final is about 2682715 and i have exception for list index when reach 2682714 with step=3

final[2682714] = OK
final[2682715] = OK
final[2682716] = ERROR

How can i handle that? we can use try/except IndexError but whole item will be ignored

Upvotes: 0

Views: 745

Answers (3)

TheQuestioner
TheQuestioner

Reputation: 771

you can use list comprehension:

final = (1, 2, 3, 4, 5, 7, 8, 9, 10, 11, 12, 13, 14, 15)
ar = []
ar = [final[i:i + 3] for i in range(0, len(final), 3)]
print(ar)

output:

[(1, 2, 3), (4, 5, 7), (8, 9, 10), (11, 12, 13), (14, 15)]

Upvotes: 2

Patrick Artner
Patrick Artner

Reputation: 51653

final = range(31)
ar = []
for i in range(0, len(final), 3):
    ar.append(tuple(final[i:i+3]))

print(ar)

Output:

[(0, 1, 2), (3, 4, 5), (6, 7, 8), (9, 10, 11), (12, 13, 14), (15, 16, 17), (18,
19, 20), (21, 22, 23), (24, 25, 26), (27, 28, 29),(30,)]

Your list length is divisible by 3 - you last element would be the last triplet , not a tuple with only one element...

Mine is not divisible by 3 without rest, so I have an incomplete tuple at the end.

Using the list comprehension tuple(final[i:i+3]) will ensure you do not overstep the boundaries of final and the remaining 1 or 2 numbers are in the last tuple.

Upvotes: 3

f5r5e5d
f5r5e5d

Reputation: 3706

slicing is nice, for one line add a zip

a = [*range(9)]

[*zip(a[::3], a[1::3], a[2::3])]

Out[321]: [(0, 1, 2), (3, 4, 5), (6, 7, 8)]

zip automatically drops extra elements that don't make up a tripple

Upvotes: 2

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