Correct the sequence index check for set and delete operations.

Usage of an index does not always imply __getitem__.

3 files changed, 97 insertions, 11 deletions

diff --git a/checkers/typecheck.py b/checkers/typecheck.py
index d3a1aae..169abda 100644
--- a/checkers/typecheck.py
+++ b/checkers/typecheck.py
@@ -540,28 +540,39 @@ accessed. Python regular expressions are accepted.'}
         if not parent_type:
             return
 
-        # Check if this instance has a __getitem__ method implemented
-        # in a bulitin sequence type. This way we catch subclasses of
-        # sequence types but skip classes that override __getitem__ and
-        # which may allow non-integer indices.
+        # Determine what method on the parent this index will use
+        # The parent of this node will be a Subscript, and the parent of that
+        # node determines if the Subscript is a get, set, or delete operation.
+        operation = node.parent.parent
+        if isinstance(operation, astroid.Assign):
+            methodname = '__setitem__'
+        elif isinstance(operation, astroid.Delete):
+            methodname = '__delitem__'
+        else:
+            methodname = '__getitem__'
+
+        # Check if this instance's __getitem__, __setitem__, or __delitem__, as
+        # appropriate to the statement, is implemented in a bulitin sequence
+        # type. This way we catch subclasses of sequence types but skip classes
+        # that override __getitem__ and which may allow non-integer indices.
         try:
-            getitems = parent_type.getattr('__getitem__')
-            if getitems is astroid.YES:
+            methods = parent_type.getattr(methodname)
+            if methods is astroid.YES:
                 return
-            getitem = getitems[0]
+            itemmethod = methods[0]
         except (astroid.NotFoundError, IndexError):
             return
 
-        if not isinstance(getitem, astroid.Function):
+        if not isinstance(itemmethod, astroid.Function):
             return
 
-        if not getitem.parent:
+        if itemmethod.root().name != BUILTINS:
             return
 
-        if getitem.root().name != BUILTINS:
+        if not itemmethod.parent:
             return
 
-        if getitem.parent.name not in sequence_types:
+        if itemmethod.parent.name not in sequence_types:
             return
 
         index_type = safe_infer(node)
diff --git a/test/input/func_invalid_sequence_index.py b/test/input/func_invalid_sequence_index.py
index c1d6e72..d0c8304 100644
--- a/test/input/func_invalid_sequence_index.py
+++ b/test/input/func_invalid_sequence_index.py
@@ -120,3 +120,68 @@ def function18():
         pass
 
     return SubTupleTest()[None] # no error
+
+# Test with set and delete statements
+
+def function19():
+    """Set with None and integer indices"""
+    TESTLIST[None] = 0
+    TESTLIST[0] = 0 # no error
+
+def function20():
+    """Delete with None and integer indicies"""
+    del TESTLIST[None]
+    del TESTLIST[0] # no error
+
+def function21():
+    """Set and delete on a subclass of list"""
+    class ListTest(list):
+        """Inherit all list get/set/del handlers"""
+        pass
+    test = ListTest()
+    test[None] = 0
+    test[0] = 0 # no error
+    del test[None]
+    del test[0] # no error
+
+def function22():
+    """Get, set, and delete on a subclass of list that overrides __setitem__"""
+    class ListTest(list):
+        """Override setitem but not get or del"""
+        def __setitem__(self, key, value):
+            pass
+    test = ListTest()
+    test[None][0] = 0
+    test[0][0] = 0 # no error
+    test[None] = 0 # no error
+    test[0] = 0 # no error
+    del test[None]
+    del test[0] # no error
+
+def function23():
+    """Get, set, and delete on a subclass of list that overrides __delitem__"""
+    class ListTest(list):
+        """Override delitem but not get or set"""
+        def __delitem__(self, key):
+            pass
+    test = ListTest()
+    test[None][0] = 0
+    test[0][0] = 0 # no error
+    test[None] = 0
+    test[0] = 0 # no error
+    del test[None] # no error
+    del test[0] # no error
+
+def function24():
+    """Get, set, and delete on a subclass of list that overrides __getitem__"""
+    class ListTest(list):
+        """Override gelitem but not del or set"""
+        def __getitem__(self, key):
+            pass
+    test = ListTest()
+    test[None][0] = 0 # no error
+    test[0][0] = 0 # no error
+    test[None] = 0
+    test[0] = 0 # no error
+    del test[None]
+    del test[0] # no error
diff --git a/test/messages/func_invalid_sequence_index.txt b/test/messages/func_invalid_sequence_index.txt
index 79a5956..cc58938 100644
--- a/test/messages/func_invalid_sequence_index.txt
+++ b/test/messages/func_invalid_sequence_index.txt
@@ -6,3 +6,13 @@ E: 68:function10: Sequence index is not an int, slice, or instance with __index_
 E: 73:function11: Sequence index is not an int, slice, or instance with __index__
 E: 81:function13: Sequence index is not an int, slice, or instance with __index__
 E: 92:function15: Sequence index is not an int, slice, or instance with __index__
+E:128:function19: Sequence index is not an int, slice, or instance with __index__
+E:133:function20: Sequence index is not an int, slice, or instance with __index__
+E:142:function21: Sequence index is not an int, slice, or instance with __index__
+E:144:function21: Sequence index is not an int, slice, or instance with __index__
+E:154:function22: Sequence index is not an int, slice, or instance with __index__
+E:158:function22: Sequence index is not an int, slice, or instance with __index__
+E:168:function23: Sequence index is not an int, slice, or instance with __index__
+E:170:function23: Sequence index is not an int, slice, or instance with __index__
+E:184:function24: Sequence index is not an int, slice, or instance with __index__
+E:186:function24: Sequence index is not an int, slice, or instance with __index__