Multi tool use

Iterate over every nth element in string in loop - python

How can iterate over every second element in string ?

One way to do this would be(If I want to iterate over nth element):

sample = "This is a string"
n = 3 # I want to iterate over every third element
i = 1
for x in sample:
if i % n == 0:
# do something with x
else:
# do something else with x
i += 1


Is thery any "pythonic" way to do this? (I am pretty sure my method is not good)

for i,x in enumerate(sample,1):

3 Answers
3

If you want to do something every nth step, and something else for other cases, you could use enumerate to get the index, and use modulus:

enumerate

sample = "This is a string"
n = 3 # I want to iterate over every third element
for i,x in enumerate(sample):
if i % n == 0:
print("do something with x "+x)
else:
print("do something else with x "+x)


Note that it doesn't start at 1 but 0. Add an offset to i if you want something else.

i

To iterate on every nth element only, the best way is to use itertools.islice to avoid creating a "hard" string just to iterate on it:

itertools.islice

import itertools
for s in itertools.islice(sample,None,None,n):
print(s)


result:

T
s
s

r
g


you can use step for example sample[start:stop:step]

step

sample[start:stop:step]

If you want to iterate over every second element you can do :

sample = "This is a string"

for x in sample[::2]:
print(x)


output

T
i

s
a
s
r
n


Try using slice:

slice

sample = "This is a string"
for i in sample[slice(None,None,2)]:
print(i)


Output:

T
i

s
a
s
r
n


sample[slice(None,None,2)]

sample[::2]

slice

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