Simplify open() call by removing default mode

The open() function opens files in read-only text mode by default. Drop
the mode argument to be slightly simpler and more idiomatic.

https://docs.python.org/3/library/functions.html#open

> The default mode is 'r' (open for reading text, synonym of 'rt').

1 files changed, 1 insertions, 1 deletions

diff --git a/sphinx/ext/coverage.py b/sphinx/ext/coverage.py
index 3045c8c87..fa9fac03b 100644
--- a/sphinx/ext/coverage.py
+++ b/sphinx/ext/coverage.py
@@ -102,7 +102,7 @@ class CoverageBuilder(Builder):
         c_objects = self.env.domaindata['c']['objects']
         for filename in self.c_sourcefiles:
             undoc = set()  # type: Set[Tuple[unicode, unicode]]
-            with open(filename, 'r') as f:
+            with open(filename) as f:
                 for line in f:
                     for key, regex in self.c_regexes:
                         match = regex.match(line)