Remove 'b' from sys.stdout.mode

changelog/5257.bugfix.rst

@@ -0,0 +1 @@
+Ensure that ``sys.stdout.mode`` does not include ``'b'`` as it is a text stream.

src/_pytest/capture.py

@@ -447,6 +447,10 @@ class EncodedFile(object):
         """Ensure that file.name is a string."""
         return repr(self.buffer)
 
+    @property
+    def mode(self):
+        return self.buffer.mode.replace("b", "")
+
     def __getattr__(self, name):
         return getattr(object.__getattribute__(self, "buffer"), name)
 

testing/test_capture.py

@@ -1051,6 +1051,9 @@ class TestFDCapture(object):
             cap.done()
             pytest.raises(AttributeError, cap.suspend)
 
+    def test_capfd_sys_stdout_mode(self, capfd):
+        assert "b" not in sys.stdout.mode
+
 
 @contextlib.contextmanager
 def saved_fd(fd):