Question

I am new to Python and having a problem with the modulo.

Here is the code:

for i in range(ord('a'), ord('z')+1):
    print chr(((i+2) % 97) + 97 )

The exptected result is cdef...a. However I am not getting the desired module behavior of wrapping around once we get to z.

Answer 1

Because 97 isn’t what you want to be wrapping at – you want to be wrapping at ord('z') = 122, and then adding the value of ord('a') (97).

The full math you really need to be doing is to shift into an offset, and then back to the set. For instance…

for i in range(ord('z') - ord('a') + 1): # equivalent to range(26); i.e. 0-25
    print chr(((i+2) % 26) + ord('a')) # results in 2+97 'c', 3+97 'd', etc.

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The reason your existing code isn’t working is because your i+2 will always be greater than 97 (since your i starts at ord('a') which is 97, and goes up from there), so the % 97 is effectively just - 97, and thus your print line is effectively this:

print chr(((i+2) - 97) + 97 )

which reduces to…

print chr((i+2) - 97 + 97)

which is obviously just print chr(i+2).