Adds some debugging changes.

python/ql/src/Expressions/ExpectedMappingForFormatString.ql

@@ -13,7 +13,37 @@
 import python
 import semmle.python.strings
 
+/* modernized query
 from Expr e, ClassValue t
 where exists(BinaryExpr b | b.getOp() instanceof Mod and format_string(b.getLeft()) and e = b.getRight() and
 mapping_format(b.getLeft()) and e.pointsTo(_, t, _) and not t.isMapping())
-select e, "Right hand side of a % operator must be a mapping, not class $@.", t, t.getName()
+select e, "Right hand side of a % operator must be a mapping, not class $@.", t, t.getName()
+//*/
+
+/* original query
+from Expr e, ClassObject t
+where exists(BinaryExpr b | b.getOp() instanceof Mod and format_string(b.getLeft()) and e = b.getRight() and
+mapping_format(b.getLeft()) and e.refersTo(_, t, _) and not t.isMapping())
+select e, "Right hand side of a % operator must be a mapping, not class $@.", t, t.getName()
+//*/
+
+//* debug query
+from Expr e, ClassValue t, string s
+where any()
+  and exists(BinaryExpr b | any()
+        and b.getOp() instanceof Mod
+        and format_string(b.getLeft())
+        and e = b.getRight()
+        and mapping_format(b.getLeft())
+        and e.pointsTo().getClass() = t
+        //and not t.isMapping()
+        )
+  and if t.hasAttribute("__getitem__") then s = "yes" else s = "no"
+select
+    e
+  , "Right hand side of a % operator must be a mapping, not class $@."
+  , t
+  , t.getName()
+  , s
+  , s
+//*/

python/ql/src/semmle/python/objects/ObjectAPI.qll

@@ -403,14 +403,45 @@ class ClassValue extends Value {
         this.hasAttribute("__getitem__")
     }
     
+    /** Holds if this class is a container(). That is, does it have a __getitem__ method.*/
+    predicate isContainer() {
+        exists(this.lookup("__getitem__"))
+    }
+    
+    /** Holds if this class is probably a sequence. */
+    predicate isSequence() {
+        /* To determine whether something is a sequence or a mapping is not entirely clear,
+         * so we need to guess a bit.
+         */
+        this.getASuperType() = ClassValue::tupleType()
+        or
+        this.getASuperType() = ClassValue::list()
+        or
+        this.getASuperType() = ClassValue::rangeType()
+        or
+        this.getASuperType() = ClassValue::bytes()
+        or
+        this.getASuperType() = ClassValue::unicode()
+        or
+        /* Does this inherit from abc.Sequence? */
+        this.getASuperType().getName() = "Sequence"
+        or
+        /* Does it have an index or __reversed__ method? */
+        this.isContainer() and
+        (
+            this.hasAttribute("index") or
+            this.hasAttribute("__reversed__")
+        )
+    }
+    
     /** Holds if this class is a mapping.
      *
      * This is an attempt to translate ClassObject::isMapping()
      */
     predicate isMapping() {
-        exists(this.attr("__getitem__"))
+        this.hasAttribute("__getitem__")
         and
-        not this instanceof SequenceValue
+        not this.isSequence()
     }
 
     /** Holds if this class is a descriptor. */