Merge pull request #1438 from Bachmann1234/issue-1437

Make a good faith effort to display a bytestring when one is provided…

_pytest/python.py

@@ -1115,7 +1115,7 @@ def _idval(val, argname, idx, idfn):
     elif isinstance(val, (float, int, str, bool, NoneType)):
         return str(val)
     elif isinstance(val, REGEX_TYPE):
-        return val.pattern
+        return _escape_bytes(val.pattern) if isinstance(val.pattern, bytes) else val.pattern
     elif enum is not None and isinstance(val, enum.Enum):
         return str(val)
     elif isclass(val) and hasattr(val, '__name__'):