Saving and restoring environment variables that tend to get clobbered…

… by XMSession.

xmextras/xm.py

@@ -34,6 +34,10 @@ def XMSessionContext():
 
                     answer = session.xmpy.res['answer']
             '''
+            # Save environment variables that tend
+            # to get clobbered by XMSession.
+            saved_env_vars = {k: v for k, v in os.environ.items() if k.startswith('XM')}
+
             session = XMSession()
             session.start()
 
@@ -42,6 +46,11 @@ def XMSessionContext():
             finally:
                 session.end()
 
+                # Restore environment variables to their
+                # state from before the XMSession.
+                for k, v in saved_env_vars.items():
+                    os.environ[k] = v
+
         def info(session):
             '''
             Returns basic info about an X-Midas instance, which can be useful