Conditionally remove 'context' from kwargs in _urlopen (#25316)

* Conditionally remove 'context' from kwargs in _urlopen

Previously, 'context' is purged from kwargs in _urlopen to
conform to varying support for 'context' in different versions
of urllib. This fix tries to use 'context', and then removes
it if an exception is thrown and tries again.

* Specify error type in try statement in _urlopen

Specify TypeError when checking if 'context' is in kwargs
for _urlopen. Also, if try fails, check that 'context' is
in the error message before removing from kwargs.

lib/spack/spack/util/web.py

@@ -507,9 +507,9 @@ def _urlopen(req, *args, **kwargs):
     except AttributeError:
         pass
 
-    # We don't pass 'context' parameter because it was only introduced starting
+    # Note: 'context' parameter was only introduced starting
     # with versions 2.7.9 and 3.4.3 of Python.
-    if 'context' in kwargs:
+    if __UNABLE_TO_VERIFY_SSL:
         del kwargs['context']
 
     opener = urlopen
@@ -517,7 +517,13 @@ def _urlopen(req, *args, **kwargs):
         import spack.s3_handler
         opener = spack.s3_handler.open
 
-    return opener(req, *args, **kwargs)
+    try:
+        return opener(req, *args, **kwargs)
+    except TypeError as err:
+        # If the above fails because of 'context', call without 'context'.
+        if 'context' in kwargs and 'context' in str(err):
+            del kwargs['context']
+        return opener(req, *args, **kwargs)
 
 
 def find_versions_of_archive(