First commit of file-contents-sorter precommit hook

pre_commit_hooks/file_contents_sorter.py

@@ -0,0 +1,57 @@
+"""
+A very simple pre-commit hook that, when passed one or more filenames
+as arguments, will sort the lines in those files.
+
+An example use case for this: you have a deploy-whitelist.txt file
+in a repo that contains a list of filenames that is used to specify
+files to be included in a docker container. This file has one filename
+per line. Various users are adding/removing lines from this file; using
+this hook on that file should reduce the instances of git merge
+conflicts and keep the file nicely ordered.
+"""
+from __future__ import print_function
+
+import argparse
+
+PASS = 0
+FAIL = 1
+
+
+def sort_file_contents(f):
+    before = [line for line in f]
+    after = sorted(before)
+
+    before_string = b''.join(before)
+    after_string = b''.join(after)
+
+    if before_string == after_string:
+        return PASS
+    else:
+        f.seek(0)
+        f.write(after_string)
+        f.truncate()
+        return FAIL
+
+
+def parse_commandline_input(argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument('filenames', nargs='+', help='Files to sort')
+    args = parser.parse_args(argv)
+    return args
+
+
+def main(argv=None):
+    args = parse_commandline_input(argv)
+
+    retv = PASS
+
+    for arg in args.filenames:
+        with open(arg, 'rb+') as file_obj:
+            ret_for_file = sort_file_contents(file_obj)
+
+            if ret_for_file:
+                print('Sorting {}'.format(arg))
+
+            retv |= ret_for_file
+
+    return retv