Prefer builtin open() over io.open() and codecs.open()

In Python3, the functions io.open() is an alias of the builtin open()
and codecs.open() is functionally equivalent. To reduce indirection,
number of imports, and number of patterns, always prefer the builtin.

https://docs.python.org/3/library/io.html#high-level-module-interface

> io.open()
>
> This is an alias for the builtin open() function.

1 files changed, 2 insertions, 3 deletions

diff --git a/sphinx/util/fileutil.py b/sphinx/util/fileutil.py
index fcbc8abe6..85b6d4f47 100644
--- a/sphinx/util/fileutil.py
+++ b/sphinx/util/fileutil.py
@@ -10,7 +10,6 @@
 """
 from __future__ import absolute_import
 
-import codecs
 import os
 import posixpath
 
@@ -49,10 +48,10 @@ def copy_asset_file(source, destination, context=None, renderer=None):
             from sphinx.util.template import SphinxRenderer
             renderer = SphinxRenderer()
 
-        with codecs.open(source, 'r', encoding='utf-8') as fsrc:  # type: ignore
+        with open(source, 'r', encoding='utf-8') as fsrc:  # type: ignore
             if destination.lower().endswith('_t'):
                 destination = destination[:-2]
-            with codecs.open(destination, 'w', encoding='utf-8') as fdst:  # type: ignore
+            with open(destination, 'w', encoding='utf-8') as fdst:  # type: ignore
                 fdst.write(renderer.render_string(fsrc.read(), context))
     else:
         copyfile(source, destination)