What do you think about this: https://bitbucket.org/jaraco/cpython-issue10639/changeset/ea63310dddce

The patch is a little more intrusive than the Python 3 patch because Python 2.7 doesn't allow specifying the newline to use when writing a file (afaict), but it abstracts that intrusiveness in the NewlineAdapter class.

I've tested the script on a file with mixed newlines, a file with non-native newlines, and a file with content but no newlines, and it performs as expected.