make except-as delete the target after the except clause

Cython/Compiler/FlowControl.py

@@ -1098,6 +1098,8 @@ class ControlFlowAnalysis(CythonTransform):
             if clause.target:
                 self.mark_assignment(clause.target)
             self.visit(clause.body)
+            if clause.is_except_as:
+                self.flow.mark_deletion(clause.target, clause.target.entry)
             if self.flow.block:
                 self.flow.block.add_child(next_block)
 

Cython/Compiler/Nodes.py

@@ -6033,6 +6033,7 @@ class ExceptClauseNode(Node):
     #  exc_value      ExcValueNode       used internally
     #  function_name  string             qualified name of enclosing function
     #  exc_vars       (string * 3)       local exception variables
+    #  is_except_as   bool               Py3-style "except ... as xyz"
 
     # excinfo_target is never set by the parser, but can be set by a transform
     # in order to extract more extensive information about the exception as a
@@ -6042,6 +6043,7 @@ class ExceptClauseNode(Node):
 
     exc_value = None
     excinfo_target = None
+    is_except_as = False
 
     def analyse_declarations(self, env):
         if self.target:
@@ -6089,11 +6091,16 @@ class ExceptClauseNode(Node):
         else:
             code.putln("/*except:*/ {")
 
-        if not getattr(self.body, 'stats', True) and \
-                self.excinfo_target is None and self.target is None:
+        if (not getattr(self.body, 'stats', True)
+                and self.excinfo_target is None
+                and (self.target is None or self.is_except_as)):
             # most simple case: no exception variable, empty body (pass)
             # => reset the exception state, done
             code.putln("PyErr_Restore(0,0,0);")
+            if self.is_except_as and self.target:
+                # "except ... as x" deletes x after use
+                # target is known to be a NameNode
+                self.target.generate_deletion_code(code)
             code.put_goto(end_label)
             code.putln("}")
             return
@@ -6133,6 +6140,10 @@ class ExceptClauseNode(Node):
             self.excinfo_tuple.generate_disposal_code(code)
         for var in exc_vars:
             code.put_decref_clear(var, py_object_type)
+        if self.is_except_as and self.target:
+            # "except ... as x" deletes x after use
+            # target is known to be a NameNode
+            self.target.generate_deletion_code(code)
         code.put_goto(end_label)
 
         if code.label_used(code.break_label):
@@ -6141,6 +6152,8 @@ class ExceptClauseNode(Node):
                 self.excinfo_tuple.generate_disposal_code(code)
             for var in exc_vars:
                 code.put_decref_clear(var, py_object_type)
+            if self.is_except_as and self.target:
+                self.target.generate_deletion_code(code)
             code.put_goto(old_break_label)
         code.break_label = old_break_label
 
@@ -6150,6 +6163,8 @@ class ExceptClauseNode(Node):
                 self.excinfo_tuple.generate_disposal_code(code)
             for var in exc_vars:
                 code.put_decref_clear(var, py_object_type)
+            if self.is_except_as and self.target:
+                self.target.generate_deletion_code(code)
             code.put_goto(old_continue_label)
         code.continue_label = old_continue_label
 

Cython/Compiler/Parsing.py

@@ -1565,6 +1565,7 @@ def p_except_clause(s):
     s.next()
     exc_type = None
     exc_value = None
+    is_except_as = False
     if s.sy != ':':
         exc_type = p_test(s)
         # normalise into list of single exception tests
@@ -1572,7 +1573,7 @@ def p_except_clause(s):
             exc_type = exc_type.args
         else:
             exc_type = [exc_type]
-        if s.sy == ',' or (s.sy == 'IDENT' and s.systring == 'as'):
+        if s.sy == ',':
             s.next()
             exc_value = p_test(s)
         elif s.sy == 'IDENT' and s.systring == 'as':
@@ -1581,9 +1582,11 @@ def p_except_clause(s):
             pos2 = s.position()
             name = p_ident(s)
             exc_value = ExprNodes.NameNode(pos2, name = name)
+            is_except_as = True
     body = p_suite(s)
     return Nodes.ExceptClauseNode(pos,
-        pattern = exc_type, target = exc_value, body = body)
+        pattern = exc_type, target = exc_value,
+        body = body, is_except_as=is_except_as)
 
 def p_include_statement(s, ctx):
     pos = s.position()

tests/run/moduletryexcept.pyx

@@ -13,6 +13,11 @@ __doc__ = u"""
 'ValueError'
 >>> exc[3] is val
 True
+
+>>> except_as_deletes
+True
+>>> no_match_does_not_delete
+True
 """
 
 a = 0
@@ -48,8 +53,9 @@ except KeyError       as e:
 except IndexError     as e:
     exc[0] = e
 except:
-    exc[0] = e
+    exc[0] = 'SOMETHING ELSE'
 
+e = None
 try:
     raise KeyError
 except AttributeError as e:
@@ -59,7 +65,23 @@ except KeyError       as e:
 except IndexError     as e:
     exc[1] = e
 except:
-    exc[1] = e
+    exc[1] = 'SOMETHING ELSE'
+
+try:
+    e
+except NameError:
+    except_as_deletes = True
+else:
+    except_as_deletes = False
+
+e = 123
+try:
+    raise TypeError
+except NameError as e:
+    pass
+except TypeError:
+    pass
+no_match_does_not_delete = (e == 123)
 
 try:
     raise IndexError
@@ -70,7 +92,7 @@ except KeyError       as e:
 except IndexError     as e:
     exc[2] = e
 except:
-    exc[2] = e
+    exc[2] = 'SOMETHING ELSE'
 
 val = None
 try:

tests/run/tryexcept.pyx

@@ -343,6 +343,47 @@ def except_as_raise(x, a):
         assert isinstance(b, a)
     return i
 
+def except_as_no_raise_does_not_touch_target(a):
+    """
+    >>> i,b = except_as_no_raise_does_not_touch_target(TypeError)
+    >>> i
+    1
+    >>> b
+    1
+    """
+    b = 1
+    try:
+        i = 1
+    except a as b:
+        i = 2
+    return i, b
+
+def except_as_raise_deletes_target(x, a):
+    """
+    >>> except_as_raise_deletes_target(None, TypeError)
+    1
+    1
+    >>> except_as_raise_deletes_target(TypeError('test'), TypeError)
+    Traceback (most recent call last):
+    UnboundLocalError: local variable 'b' referenced before assignment
+    >>> except_as_raise_deletes_target(ValueError('test'), TypeError)
+    Traceback (most recent call last):
+    ValueError: test
+    >>> except_as_raise_deletes_target(None, TypeError)
+    1
+    1
+    """
+    b = 1
+    try:
+        i = 1
+        if x:
+            raise x
+    except a as b:
+        i = 2
+        assert isinstance(b, a)
+    print(b)  # raises NameError if except clause was executed
+    return i
+
 def complete_except_as_no_raise(a, b):
     """
     >>> complete_except_as_no_raise(TypeError, ValueError)