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
echo "nothing" > a
hg add a
hg commit -m ancestor -d "1000000 0"
echo "something" > a
hg commit -m branch1 -d "1000000 0"
hg co 0
echo "something else" > a
hg commit -m branch2 -d "1000000 0"
HGMERGE=merge; export HGMERGE
hg merge 1
hg id
egrep -v ">>>|<<<" a
hg status