Fix pylint-dev#2615 -- Extend solution to Except Handlers

Also fix bug where different TryFinally nodes were mixed up

Author: jacobtylerwalls

ChangeLog

@@ -9,11 +9,10 @@ Release date: TBA
 ..
   Put new features here and also in 'doc/whatsnew/2.13.rst'
 
-* ``used-before-assignment`` now considers that assignments in the try block
-  of a try/finally clause may not have occurred when the final block is
-  executed.
+* ``used-before-assignment`` now considers that assignments in a try block
+  may not have occurred when the except or finally blocks are executed.
 
-  Closes #85
+  Closes #85, #2615
 
 ..
   Insert your changelog randomly, it will reduce merge conflicts

doc/whatsnew/2.13.rst

@@ -24,8 +24,7 @@ Other Changes
 
   Closes #5065
 
-* ``used-before-assignment`` now considers that assignments in the try block
-  of a try/finally clause may not have occurred when the final block is
-  executed.
+* ``used-before-assignment`` now considers that assignments in a try block
+  may not have occurred when the except or finally blocks are executed.
 
-  Closes #85
+  Closes #85, #2615

pylint/checkers/variables.py

@@ -392,7 +392,7 @@ def _has_locals_call_after_node(stmt, scope):
         "Using variable %r before assignment",
         "used-before-assignment",
         "Used when a local variable is accessed before its assignment or in "
-        "a finally block without being defined outside the try block.",
+        "except or finally blocks without being defined before the try block.",
     ),
     "E0602": (
         "Undefined variable %r",
@@ -622,14 +622,32 @@ def get_next_to_consume(self, node):
                 n
                 for n in found_nodes
                 if not (
-                    isinstance(n.statement(future=True).parent, nodes.TryFinally)
+                    n.statement(future=True).parent is node.statement(future=True).parent
                     and n.statement(future=True) in n.statement(future=True).parent.body
                 )
             ]
             difference = set(found_nodes) - set(filtered_nodes)
             self.mark_as_consumed(name, difference)
             found_nodes = filtered_nodes
 
+        # If this node is in an ExceptHandler,
+        # filter out assignments in the try portion, assuming they may fail
+        if found_nodes and isinstance(
+            node.statement(future=True).parent, nodes.ExceptHandler
+        ):
+            filtered_nodes = [
+                n
+                for n in found_nodes
+                if not (
+                    isinstance(n.statement(future=True).parent, nodes.TryExcept)
+                    and n.statement(future=True) in n.statement(future=True).parent.body
+                    and node.statement(future=True).parent in n.statement(future=True).parent.handlers
+                )
+            ]
+            difference = set(found_nodes) - set(filtered_nodes)
+            self.mark_as_consumed(name, difference)
+            found_nodes = filtered_nodes
+
         return found_nodes
 
 

tests/functional/u/use/used_before_assignment_issue2615.py

@@ -0,0 +1,9 @@
+"""https://github.com/PyCQA/pylint/issues/2615"""
+def main():
+    """When evaluating except blocks, assume try statements fail."""
+    try:
+        res = 1 / 0
+        res = 42
+    except ZeroDivisionError:
+        print(res)  # [used-before-assignment]
+    print(res)

tests/functional/u/use/used_before_assignment_issue2615.txt

@@ -0,0 +1 @@
+used-before-assignment:8:14:8:17:main:Using variable 'res' before assignment:UNDEFINED