Merge #424

424: Do not attempt to close an already closed resources in __del__ r=MatthieuDartiailh a=MatthieuDartiailh

This can mitigate issues such as #416.

Co-authored-by: MatthieuDartiailh <marul@laposte.net>
Co-authored-by: Matthieu Dartiailh <marul@laposte.net>

CHANGES

@@ -4,6 +4,7 @@ PyVISA Changelog
 1.10 (unreleased)
 -----------------
 
+- avoid attempting to close already closed resources in del PR #424
 - add a list_opened_resources method to the ResourceManager PR #415
 - use privately stored resource name in Resource class rather than relying on
   VisaLibrary PR #415

pyvisa/highlevel.py

@@ -1587,7 +1587,8 @@ def __repr__(self):
         return '<ResourceManager(%r)>' % self.visalib
 
     def __del__(self):
-        self.close()
+        if self._session is not None:
+            self.close()
 
     def ignore_warning(self, *warnings_constants):
         """Ignoring warnings context manager for the current resource.
@@ -1606,6 +1607,7 @@ def last_status(self):
 
     def close(self):
         """Close the resource manager session.
+
         """
         try:
             logger.debug('Closing ResourceManager (session: %s)', self.session)

pyvisa/resources/resource.py

@@ -110,7 +110,8 @@ def session(self, value):
         self._session = value
 
     def __del__(self):
-        self.close()
+        if self._session is not None:
+            self.close()
 
     def __str__(self):
         return "%s at %s" % (self.__class__.__name__, self._resource_name)