Better fix for handling of static CO attribute values.

SATOSA internal attribute values are of type list because some
attributes can have multiple values. This fix works for Python 3.4 and
above but should be refactored when Python 3.4 support is no longer
required.

Author: skoranda

src/satosa/frontends/saml2.py

@@ -14,7 +14,6 @@
 from urllib.parse import unquote_plus
 from urllib.parse import urlparse
 from http.cookies import SimpleCookie
-from typing import Iterable
 
 from saml2 import SAMLError, xmldsig
 from saml2.config import IdPConfig
@@ -743,12 +742,15 @@ def _handle_authn_response(self, context, internal_response):
         if self.KEY_CO_ATTRIBUTES in co_config:
             attributes = internal_response.attributes
             for attribute, value in co_config[self.KEY_CO_ATTRIBUTES].items():
-                attributes[attribute] = (
-                    value                           # keep the value as is
-                    if isinstance(value, Iterable)  # if it is already a list
-                    and not isinstance(value, str)  # and not a string
-                    else [value]                    # otherwise wrap in a list
-                )
+                # This should be refactored when Python 3.4 support is
+                # no longer required to use isinstance(value, Iterable).
+                try:
+                    if iter(value) and not isinstance(value, str):
+                        attributes[attribute] = value
+                    else:
+                        attributes[attribute] = [value]
+                except TypeError:
+                        attributes[attribute] = [value]
 
         # Handle the authentication response.
         return super()._handle_authn_response(context, internal_response, idp)