How to use enumerate and slicing together

Question

The following is the normal usage of enumerate for the case that i want to have every 10 items:

for index, value in enumerate(range(50)):
    if index % 10 == 0:
        print(index,value)

Output:

0 0
10 10
20 20
30 30
40 40

now imagine i want to have output as:

1 1
11 11
21 21
31 31
41 41

or

2 2
12 12
22 22
32 32
42 42

How I can do that?

Answer 1

Not sure why you are doing it this way but you can just subtract n from index in the test, e.g.:

In []:
n = 1
for index, value in enumerate(range(50)):
    if (index-n) % 10 == 0:
        print(index,value)

Out[]:
1 1
11 11
21 21
31 31
41 41

Just set n=2 for your second case and if course n=0 is the base case.

Alternatively, just start from -n in enumerate, which gives you the right values (but different index):

In []:
n = 1
for index, value in enumerate(range(50), -n):
    if index % 10 == 0:
        print(index,value)

Out[]:
0 1
10 11
20 21
30 31
40 41

But you really don't need to enumerate and % the index to get every 10th value, assuming you want to work on any iterable just use itertools.islice(), e.g.

In []:
import itertools as it
n = 0
for value in it.islice(range(50), n, None, 10):
    print(value)

Out[]:
0
10
20
30
40

Then just change the value of n, e.g.:

In []:
n = 1
for value in it.islice(range(50), n, None, 10):
    print(value)

Out[]:
1
11
21
31
41