The last except handler wins when inferring variables bound in an except handler.

Close pylint-dev/pylint#2777

Author: PCManticore

ChangeLog

@@ -42,6 +42,10 @@ Release Date: 2019-03-02
  Close PyCQA/pylint#2776
 
 
+* The last except handler wins when inferring variables bound in an except handler.
+
+  Close PyCQA/pylint#2777
+
 What's New in astroid 2.2.0?
 ============================
 Release Date: 2019-02-27

astroid/node_classes.py

@@ -1096,6 +1096,16 @@ def ilookup(self, name):
         context = contextmod.InferenceContext()
         return bases._infer_stmts(stmts, context, frame)
 
+    def _get_filtered_node_statements(self, nodes):
+        statements = {node: node.statement() for node in nodes}
+        # Next we check if we have ExceptHandlers that are parent
+        # of the underlying variable, in which case the last one survives
+        if all(isinstance(stmt, ExceptHandler) for stmt in statements.values()):
+            statements = {
+                node: stmt for node, stmt in statements.items() if stmt.parent_of(self)
+            }
+        return statements
+
     def _filter_stmts(self, stmts, frame, offset):
         """Filter the given list of statements to remove ignorable statements.
 
@@ -1149,10 +1159,12 @@ def _filter_stmts(self, stmts, frame, offset):
         else:
             # disabling lineno filtering
             mylineno = 0
+
         _stmts = []
         _stmt_parents = []
-        for node in stmts:
-            stmt = node.statement()
+        statements = self._get_filtered_node_statements(stmts)
+
+        for node, stmt in statements.items():
             # line filtering is on and we have reached our location, break
             if stmt.fromlineno > mylineno > 0:
                 break

astroid/tests/unittest_inference.py

@@ -5090,5 +5090,64 @@ def test(self):
     assert isinstance(inferred, Slice)
 
 
+def test_exception_lookup_last_except_handler_wins():
+    node = extract_node(
+        """
+    try:
+        1/0
+    except ValueError as exc:
+        pass
+    try:
+        1/0
+    except OSError as exc:
+        exc #@
+    """
+    )
+    inferred = node.inferred()
+    assert len(inferred) == 1
+    inferred_exc = inferred[0]
+    assert isinstance(inferred_exc, Instance)
+    assert inferred_exc.name == "OSError"
+
+    # Check that two except handlers on the same TryExcept works the same as separate
+    # TryExcepts
+    node = extract_node(
+        """
+    try:
+        1/0
+    except ZeroDivisionError as exc:
+        pass
+    except ValueError as exc:
+        exc #@
+    """
+    )
+    inferred = node.inferred()
+    assert len(inferred) == 1
+    inferred_exc = inferred[0]
+    assert isinstance(inferred_exc, Instance)
+    assert inferred_exc.name == "ValueError"
+
+
+def test_exception_lookup_name_bound_in_except_handler():
+    node = extract_node(
+        """
+    try:
+        1/0
+    except ValueError:
+        name = 1
+    try:
+        1/0
+    except OSError:
+        name = 2
+        name #@
+    """
+    )
+    inferred = node.inferred()
+    assert len(inferred) == 1
+    inferred_exc = inferred[0]
+    assert isinstance(inferred_exc, nodes.Const)
+    assert inferred_exc.value == 2
+
+
 if __name__ == "__main__":
     unittest.main()