Create test expectations line automatically from failing test results

third_party/WebKit/Tools/Scripts/update-w3c-test-expections

+#!/usr/bin/env python
+# Copyright 2016 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import sys
+
+from webkitpy.common import host
+from webkitpy.common.checkout.scm.git import Git
+from webkitpy.w3c.update_w3c_test_expectations import main
+
+if __name__ == "__main__":
+    host = host.Host()
+    host.initialize_scm()
+    port = host.port_factory.get()
+    return_code = main(host, port)
+
+sys.exit(return_code)

[Dirk Pranke, 2016/08/09 03:59:39]

this line probably should've been combined with line 16:

  sys.exit(main(host, port))

as it is, if this file was somehow eval'ed directly, it wouldn't work right and
would always call sys.exit(), but with an uninitialized variable.

[dcampb, 2016/08/09 18:10:44]

What do you mean by eval'ed directly?? I'm a little confused.

[Dirk Pranke, 2016/08/09 18:35:04]

Good question, I wasn't super clear here ... I'm talking about what Python does
when a file is loaded.

If, for example, this file was a python module that got imported, and not a
top-level script, then

if you were to run `python update_w3c_test_expectations.py`, __name__ would be
set to "__main__"
and the block on lines 12-16 would execute, as would line 18, so things would be
fine.

However, if you were to run another python file that had `import
update_w3_test_expectations`,
__name__ would *not* be set to "__main__", so that block wouldn't execute, but
line 18 would 
still execute. Which would be even worse, since that would cause python to quit
(both because
of the uninitialized variable and because you're calling sys.exit()).

Of course, this isn't a module, it's a top-level script. So, you can't import
it, and don't have that
problem, but you could still call execfile("update-w3-test-expectations") and
the same thing would
happen. Though it's not real likely that anyone's going to do this, either. So
this isn't a bug that's
likely to actually show up.

This is a long winded-way of saying be careful what you have as unindented
python code in
scripts, because it'll always execute, and be careful about what you have in 
`if __name__ == "__main__"` blocks :).

[dcampb, 2016/08/09 18:49:50]

So should I unindent the block and remove the 'if __name__ == "__main__"' line??
and add sys.exit(main(host, port))? 
I reckon this would run no matter what calls it?