Add encoding pragma hook. Resolves pre-commit/pre-commit#15

pre_commit_hooks/fix_encoding_pragma.py

@@ -0,0 +1,75 @@
+from __future__ import absolute_import
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import argparse
+import io
+
+expected_pragma = b'# -*- coding: utf-8 -*-\n'
+
+
+def has_coding(line):
+    if not line.strip():
+        return False
+    return (
+        line.lstrip()[0:1] == b'#' and (
+            b'unicode' in line or
+            b'encoding' in line or
+            b'coding:' in line or
+            b'coding=' in line
+        )
+    )
+
+
+def fix_encoding_pragma(f):
+    first_line = f.readline()
+    second_line = f.readline()
+    old = f.read()
+    f.seek(0)
+
+    # Ok case: the file is empty
+    if not (first_line + second_line + old).strip():
+        return 0
+
+    # Ok case: we specify pragma as the first line
+    if first_line == expected_pragma:
+        return 0
+
+    # OK case: we have a shebang as first line and pragma on second line
+    if first_line.startswith(b'#!') and second_line == expected_pragma:
+        return 0
+
+    # Otherwise we need to rewrite stuff!
+    if first_line.startswith(b'#!'):
+        if has_coding(second_line):
+            f.write(first_line + expected_pragma + old)
+        else:
+            f.write(first_line + expected_pragma + second_line + old)
+    elif has_coding(first_line):
+        f.write(expected_pragma + second_line + old)
+    else:
+        f.write(expected_pragma + first_line + second_line + old)
+
+    return 1
+
+
+def main(argv=None):
+    parser = argparse.ArgumentParser('Fixes the encoding pragma of python files')
+    parser.add_argument('filenames', nargs='*', help='Filenames to fix')
+    args = parser.parse_args(argv)
+
+    retv = 0
+
+    for filename in args.filenames:
+        with io.open(filename, 'r+b') as f:
+            file_ret = fix_encoding_pragma(f)
+            retv |= file_ret
+            if file_ret:
+                print('Added `{0}` to {1}'.format(
+                    expected_pragma.strip(), filename,
+                ))
+
+    return retv
+
+if __name__ == "__main__":
+    exit(main())