Bugfix urlparse in python >= 3.7.6

[gmossessian]

In Python 3.7.6, a patch has been released that changes the behavior of urllib.parse.urlparse. This causes an error when pushing to a gateway without a scheme specified in the url string, but with a port.

Patch details here: https://bugs.python.org/issue27657

Proof of failure on my local branch:

client_python gmoss$ python3 --version
Python 3.7.6



client_python gmoss$ git diff
diff --git a/prometheus_client/exposition.py b/prometheus_client/exposition.py
index 4cac223..5c2b8b1 100644
--- a/prometheus_client/exposition.py
+++ b/prometheus_client/exposition.py
@@ -30,7 +30,7 @@ CONTENT_TYPE_LATEST = str('text/plain; version=0.0.4; charset=utf-8')
 
 PYTHON26_OR_OLDER = sys.version_info < (2, 7)
 # Due to https://bugs.python.org/issue27657:
-PYTHON376_OR_NEWER = sys.version_info > (3, 7, 5)
+PYTHON376_OR_NEWER = False  # sys.version_info > (3, 7, 5)
 
 def make_wsgi_app(registry=REGISTRY):
     """Create a WSGI app which serves the metrics from a registry."""



client_python gmoss$ python3 -m pytest tests/test_exposition.py::TestPushGateway::test_push_schemeless_url
======================================================================================================== test session starts ========================================================================================================
platform darwin -- Python 3.7.6, pytest-5.3.2, py-1.8.0, pluggy-0.13.1
rootdir: /Users/gmoss/Documents/constructor/client_python
collected 1 item                                                                                                                                                                                                                    

tests/test_exposition.py F                                                                                                                                                                                                    [100%]

============================================================================================================= FAILURES ==============================================================================================================
_____________________________________________________________________________________________ TestPushGateway.test_push_schemeless_url ______________________________________________________________________________________________

self = <tests.test_exposition.TestPushGateway testMethod=test_push_schemeless_url>

    def test_push_schemeless_url(self):
>       push_to_gateway(self.address.replace('http://', ''), "my_job", self.registry)

tests/test_exposition.py:239: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
prometheus_client/exposition.py:290: in push_to_gateway
    _use_gateway('PUT', gateway, job, registry, grouping_key, timeout, handler)
prometheus_client/exposition.py:364: in _use_gateway
    headers=[('Content-Type', CONTENT_TYPE_LATEST)], data=data,
prometheus_client/exposition.py:222: in handle
    resp = build_opener(HTTPHandler).open(request, timeout=timeout)
/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/urllib/request.py:525: in open
    response = self._open(req, data)
/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/urllib/request.py:548: in _open
    'unknown_open', req)
/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/urllib/request.py:503: in _call_chain
    result = func(*args)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <urllib.request.UnknownHandler object at 0x1022c35d0>, req = <urllib.request.Request object at 0x1022c3310>

    def unknown_open(self, req):
        type = req.type
>       raise URLError('unknown url type: %s' % type)
E       urllib.error.URLError: <urlopen error unknown url type: localhost>

/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/urllib/request.py:1389: URLError
========================================================================================================= 1 failed in 0.32s =========================================================================================================

[brian-brazil]

I'd put this comment down where you use it

[gmossessian]

Done in 41a1831

[brian-brazil]

Thanks!