Add hook for checking python modules

pre_commit_hooks/check_python_modules.py

@@ -0,0 +1,50 @@
+from __future__ import absolute_import
+from __future__ import print_function
+
+import os.path
+from argparse import ArgumentParser
+from typing import Optional
+from typing import Sequence
+from typing import Set
+
+OK = 0
+ERR = 1
+
+
+class ModuleInitChecker:
+    def __init__(self):
+        # type: () -> None
+        self.seen_dirnames = set()  # type: Set[str]
+
+    def check(self, filename):
+        # type: (str) -> int
+        dirname = os.path.dirname(filename)
+        if dirname in self.seen_dirnames:
+            return OK
+
+        init_file = os.path.join(dirname, '__init__.py')
+        if dirname and not os.path.exists(init_file):
+            self.seen_dirnames.add(dirname)
+            with open(init_file, 'w'):
+                print(f'Created {init_file}')
+                return ERR
+
+        return OK
+
+
+def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
+    parser = ArgumentParser()
+    parser.add_argument('filenames', nargs='*')
+
+    args = parser.parse_args(argv)
+
+    status = OK
+    checker = ModuleInitChecker()
+    for filename in args.filenames:
+        status |= checker.check(filename)
+
+    return status
+
+
+if __name__ == '__main__':
+    exit(main())