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, 7 insertions, 6 deletions

diff --git a/sphinx/builders/changes.py b/sphinx/builders/changes.py
index 3f9bffa0d..d5244747d 100644
--- a/sphinx/builders/changes.py
+++ b/sphinx/builders/changes.py
@@ -9,7 +9,6 @@
     :license: BSD, see LICENSE for details.
 """
 
-import codecs
 from os import path
 from typing import cast
 
@@ -115,9 +114,11 @@ class ChangesBuilder(Builder):
             'show_copyright': self.config.html_show_copyright,
             'show_sphinx': self.config.html_show_sphinx,
         }
-        with codecs.open(path.join(self.outdir, 'index.html'), 'w', 'utf8') as f:  # type: ignore  # NOQA
+        with open(path.join(self.outdir, 'index.html'), 'w',  # type: ignore
+                  encoding='utf8') as f:
             f.write(self.templates.render('changes/frameset.html', ctx))
-        with codecs.open(path.join(self.outdir, 'changes.html'), 'w', 'utf8') as f:  # type: ignore  # NOQA
+        with open(path.join(self.outdir, 'changes.html'), 'w',  # type: ignore
+                  encoding='utf8') as f:
             f.write(self.templates.render('changes/versionchanges.html', ctx))
 
         hltext = ['.. versionadded:: %s' % version,
@@ -135,8 +136,8 @@ class ChangesBuilder(Builder):
 
         logger.info(bold(__('copying source files...')))
         for docname in self.env.all_docs:
-            with codecs.open(self.env.doc2path(docname), 'r',  # type: ignore
-                             self.env.config.source_encoding) as f:
+            with open(self.env.doc2path(docname), 'r',  # type: ignore
+                      encoding=self.env.config.source_encoding) as f:
                 try:
                     lines = f.readlines()
                 except UnicodeDecodeError:
@@ -144,7 +145,7 @@ class ChangesBuilder(Builder):
                     continue
             targetfn = path.join(self.outdir, 'rst', os_path(docname)) + '.html'
             ensuredir(path.dirname(targetfn))
-            with codecs.open(targetfn, 'w', 'utf-8') as f:  # type: ignore
+            with open(targetfn, 'w', encoding='utf-8') as f:  # type: ignore
                 text = ''.join(hl(i + 1, line) for (i, line) in enumerate(lines))
                 ctx = {
                     'filename': self.env.doc2path(docname, None),