More robust inspector handling of objects for which vars() fails (#7)

Objects without `__dict__`, like ones using `__slots__`, caused an exception message to be printed.

tracerite/inspector.py

@@ -39,7 +39,7 @@ def extract_variables(variables, sourcecode):
             # Try to print members of objects that don't have proper __str__
             elif no_str_conv.fullmatch(strvalue):
                 found = False
-                for n, v in vars(value).items():
+                for n, v in safe_vars(value).items():
                     mname = f'{name}.{n}'
                     if sourcecode and mname not in identifiers:
                         continue
@@ -73,6 +73,17 @@ def extract_variables(variables, sourcecode):
     return rows
 
 
+def safe_vars(obj):
+    """Like vars(), but also supports objects with slots."""
+    ret = {}
+    for attr in dir(obj):
+        try:
+            ret[attr] = object.__getattribute__(obj, attr)
+        except AttributeError:
+            pass  # Slots that haven't been set
+    return ret
+
+
 def prettyvalue(val):
     if isinstance(val, (list, tuple)):
         if not 0 < len(val) <= 10: