use __contains__, index or split instead of str.find str.find return -1 when the substring is not found, -1 evaluate to True and is a valid index, which can lead to bugs. Using alternatives when possible makes the code clearer and less prone to bugs. (and __contains__ is faster in microbenchmarks)

#!/bin/sh

hg init a
cd a
hg init b
echo x > b/x
echo '# should print nothing'
hg st
echo '# should print ? b/x'
hg st b/x

hg add b/x

echo '# should print A b/x'
hg st
echo '# should forget b/x'
hg revert
echo '# should print nothing'
hg st b