With meu 1.5.0 should work on py3.

mercurial_keyring.py

@@ -447,11 +447,9 b' class HTTPPasswordHandler(object):'
         found. username and password can be None (if unset), if prefix
         is not found, url itself is returned.
         """
-        base_url = bytes(parsed_url)
-
         from mercurial.httpconnection import readauthforuri
-        ui.debug(b"keyring: checking for hgrc info about url %s, user %s\n" % (base_url, user))
-        res = readauthforuri(ui, base_url, user)
+        ui.debug(b"keyring: checking for hgrc info about url %s, user %s\n" % (parsed_url, user))
+        res = readauthforuri(ui, str(parsed_url), user)
         # If it user-less version not work, let's try with added username to handle
         # both config conventions
         if (not res) and user:
@@ -472,7 +470,7 b' class HTTPPasswordHandler(object):'
             password = None
             prefix = None
 
-        password_url = self.password_url(base_url, prefix)
+        password_url = self.password_url(str(parsed_url), prefix)
 
         ui.debug(b"keyring: Password url: %s, user: %s, password: %s (prefix: %s)\n" % (
             password_url, username or b'', b'********' if password else b'', prefix or b''))

setup.py

@@ -36,7 +36,7 b' setup('
     ],
     install_requires=[
         'keyring>=0.3',
-        'mercurial_extension_utils>=1.3.6',
+        'mercurial_extension_utils>=1.5.0',
     ],
     zip_safe=True,
 )