optimize code in Python

Question

I created and solved a problem using Python and I would like to know if
it can be done in any way better.

We have a string where one letter needs to be replaced with a substitute,
on every position in the string from it's own possible values.
The generated strings have only one letter different from the original.

s = "aaaaa"
e = ["bcdefgh", "ijklmn", "opqrs", "tuvw", "xyz"]

i = 0
for a in e:
j = 0
for c in range(len(a)):
print(s[:i] + a[j] + s[i+1:])
j += 1
i += 1

Thank you.

Answer 1

You could also iterate over the characters of a as a list instead of iterating c over the indexes into the string like this:
s = "aaaaa"
e = ["bcdefgh", "ijklmn", "opqrs", "tuvw", "xyz"]

for i, a in enumerate(e):
for c in list(a):
print(s[:i] + c + s[i+1:])

Yes, there are lots of ways to do this even if none will significantly improve performance.

Since s is all 'a', you could also do this to get the same behaviour without having an s variable:
e = ["bcdefgh", "ijklmn", "opqrs", "tuvw", "xyz"]

for i, a in enumerate(e):
for c in list(a):
print('a' * i + c + 'a' * (4 - i))

Answer 2

The code you shared can't be made much faster without changing how it behaves.
I found a couple changes that may make the code cleaner, though.

A small improvement to clean up the code would be to remove the variable j.
j is the same as c in your nested loop so you can get the same behaviour from this code:
s = "aaaaa"
e = ["bcdefgh", "ijklmn", "opqrs", "tuvw", "xyz"]

i = 0
for a in e:
for c in range(len(a)):
print(s[:i] + a[c] + s[i+1:])
i += 1

Another minor change that just might make things cleaner is the enumerate function.
Using enumerate, you can stop calling "i = 0" and "i += 1".
Below uses enumerate and the above suggestion to remove j.
s = "aaaaa"
e = ["bcdefgh", "ijklmn", "opqrs", "tuvw", "xyz"]

for i, a in enumerate(e):
for c in range(len(a)):
print(s[:i] + a[c] + s[i+1:])

Answer 3

Thank you very much. Somehow I felt bad about using those counters in parallel with the loops.

Answer 4

@Josh Greig Using list(a) you managed to further shorten the code length but I used only 'a' in s just to make the problem look better. In the past when I had this kind of problem s was not known beforehand and also the list of values didn't look so predictable. To keep the code reusable I wouldn't look for improvements in how s and e are defined.