diff --git a/pre_commit_hooks/pretty_format_json.py b/pre_commit_hooks/pretty_format_json.py
index 7d515f4..25827dc 100644
--- a/pre_commit_hooks/pretty_format_json.py
+++ b/pre_commit_hooks/pretty_format_json.py
@@ -1,10 +1,5 @@
-from __future__ import print_function
-
 import argparse
-import io
 import json
-import sys
-from collections import OrderedDict
 from difflib import unified_diff
 from typing import List
 from typing import Mapping
@@ -13,38 +8,36 @@
 from typing import Tuple
 from typing import Union
 
-from six import text_type
-
 
 def _get_pretty_format(
-        contents, indent, ensure_ascii=True, sort_keys=True, top_keys=(),
-):  # type: (str, str, bool, bool, Sequence[str]) -> str
-    def pairs_first(pairs):
-        # type: (Sequence[Tuple[str, str]]) -> Mapping[str, str]
+        contents: str,
+        indent: str,
+        ensure_ascii: bool = True,
+        sort_keys: bool = True,
+        top_keys: Sequence[str] = (),
+) -> str:
+    def pairs_first(pairs: Sequence[Tuple[str, str]]) -> Mapping[str, str]:
         before = [pair for pair in pairs if pair[0] in top_keys]
         before = sorted(before, key=lambda x: top_keys.index(x[0]))
         after = [pair for pair in pairs if pair[0] not in top_keys]
         if sort_keys:
-            after = sorted(after, key=lambda x: x[0])
-        return OrderedDict(before + after)
+            after.sort()
+        return dict(before + after)
     json_pretty = json.dumps(
         json.loads(contents, object_pairs_hook=pairs_first),
         indent=indent,
         ensure_ascii=ensure_ascii,
-        # Workaround for https://bugs.python.org/issue16333
-        separators=(',', ': '),
     )
-    # Ensure unicode (Py2) and add the newline that dumps does not end with.
-    return text_type(json_pretty) + '\n'
+    return f'{json_pretty}\n'
 
 
-def _autofix(filename, new_contents):  # type: (str, str) -> None
-    print('Fixing file {}'.format(filename))
-    with io.open(filename, 'w', encoding='UTF-8') as f:
+def _autofix(filename: str, new_contents: str) -> None:
+    print(f'Fixing file {filename}')
+    with open(filename, 'w', encoding='UTF-8') as f:
         f.write(new_contents)
 
 
-def parse_num_to_int(s):  # type: (str) -> Union[int, str]
+def parse_num_to_int(s: str) -> Union[int, str]:
     """Convert string numbers to int, leaving strings as is."""
     try:
         return int(s)
@@ -52,18 +45,18 @@
         return s
 
 
-def parse_topkeys(s):  # type: (str) -> List[str]
+def parse_topkeys(s: str) -> List[str]:
     return s.split(',')
 
 
-def get_diff(source, target, file):  # type: (str, str, str) -> str
+def get_diff(source: str, target: str, file: str) -> str:
     source_lines = source.splitlines(True)
     target_lines = target.splitlines(True)
     diff = unified_diff(source_lines, target_lines, fromfile=file, tofile=file)
     return ''.join(diff)
 
 
-def main(argv=None):  # type: (Optional[Sequence[str]]) -> int
+def main(argv: Optional[Sequence[str]] = None) -> int:
     parser = argparse.ArgumentParser()
     parser.add_argument(
         '--autofix',
@@ -110,7 +103,7 @@
     status = 0
 
     for json_file in args.filenames:
-        with io.open(json_file, encoding='UTF-8') as f:
+        with open(json_file, encoding='UTF-8') as f:
             contents = f.read()
 
         try:
@@ -131,8 +124,8 @@
                 status = 1
         except ValueError:
             print(
-                'Input File {} is not a valid JSON, consider using check-json'
-                .format(json_file),
+                f'Input File {json_file} is not a valid JSON, consider using '
+                f'check-json',
             )
             return 1
 
@@ -140,4 +133,4 @@
 
 
 if __name__ == '__main__':
-    sys.exit(main())
+    exit(main())