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pythonstringoptimizationiteratorreverse

Best way to loop over a python string backwards

What is the best way to loop over a python string backwards?

The following seems a little awkward for all the need of -1 offset:

string = "trick or treat"
for i in range(len(string)-1, 0-1, -1):
    print string[i]

The following seems more succinct, but is it actually generate a reversed string so that there is a minor performance penalty?

string = "trick or treat"
for c in string[::-1]:
    print c
Solution

  • Try the reversed builtin:

    for c in reversed(string):
     print c

    The reversed() call will make an iterator rather than copying the entire string.

    PEP 322 details the motivation for reversed() and its advantages over other approaches.