Do not modify global context var in TLS class

Use local ssl_context variable instead of global context variable. Respect 80 columns limit and add ´param´ in front of new argument in comments

Author: jdecuyper

hyper/http20/connection.py

@@ -51,11 +51,11 @@ class HTTP20Connection(object):
     :param enable_push: (optional) Whether the server is allowed to push
         resources to the client (see
         :meth:`get_pushes() <hyper.HTTP20Connection.get_pushes>`).
-    :ssl_context: (optional) A class with custom certificate settings. If not provided
-        then hyper's default SSLContext is used instead.
+    :param ssl_context: (optional) A class with custom certificate settings.
+        If not provided then hyper's default SSLContext is used instead.
     """
-    def __init__(self, host, port=None, window_manager=None, enable_push=False, ssl_context=None,
-                 **kwargs):
+    def __init__(self, host, port=None, window_manager=None, enable_push=False,
+                 ssl_context=None, **kwargs):
         """
         Creates an HTTP/2 connection to a specific server.
         """

hyper/tls.py

@@ -31,10 +31,13 @@ def wrap_socket(sock, server_hostname, ssl_context=None):
     global _context
 
     if _context is None:  # pragma: no cover
-        _context = ssl_context or _init_context()
+        _context = _init_context()
+
+    # if an SSLContext is provided then use it instead of default context
+    _ssl_context = ssl_context or _context
 
     # the spec requires SNI support
-    ssl_sock = _context.wrap_socket(sock, server_hostname=server_hostname)
+    ssl_sock = _ssl_context.wrap_socket(sock, server_hostname=server_hostname)
     # Setting SSLContext.check_hostname to True only verifies that the
     # post-handshake servername matches that of the certificate. We also need
     # to check that it matches the requested one.