Fail if changes are required

[adamchainz]

It would be useful to use python–modernize in CI setups if it could fail when changes are required. Currently the return code is always 0 unless an error occurred during execution.

I'd suggest a --fail-if-changes-required flag, mutually exclusive with --write, that has return code 1 if changes are required.

[daira]

That sounds like a good idea. As a workaround for lack of this feature, you can use -z in bash (http://stackoverflow.com/a/12137504/393146) to check that the output of python-modernize without the --write flag is empty.

[techtonik]

Why not just return 1 if changes are required and --write is not specified?

[adamchainz]

That would be a breaking change and could disrupt many CI scripts/tools out there.