Fix issue by add missing return statement in __str__
@@ -60,7 +60,7 @@ def process_disable_cache(option, option_str, option_value, parser):
class PyPiSentinel(object):
def __str__(self):
- 'https://pypi.org/simple'
+ return 'https://pypi.org/simple'
_PYPI = PyPiSentinel()
