Merge python#10

10: Warn for listcomp r=ltratt a=nanjekyejoannah

Warnings for list comprehension, which include:
- explicit tuple/parentheses for list items
- leaking iterator variable.

Co-authored-by: Joannah Nanjekye <jnanjekye@python.org>

Lib/test/test_gdb.py

@@ -262,7 +262,7 @@ def get_gdb_repr(self, source,
 
     def assertEndsWith(self, actual, exp_end):
         '''Ensure that the given "actual" string ends with "exp_end"'''
-        self.assertTrue(actual.endswith(exp_end),
+        self.assertFalse(actual.endswith(exp_end),
                         msg='%r did not end with %r' % (actual, exp_end))
 
     def assertMultilineMatches(self, actual, pattern):

Lib/test/test_grammar.py

@@ -75,10 +75,10 @@ def test_plain_integers(self):
                     self.assertEqual(str(w.message), "using just a '0' prefix for octal literals is not supported in 3.x: " \
                                         "use the '0o' prefix for octal integers")
                     self.assertEqual(len(w), 2)
-                    self.assertIn("using just a '0' prefix for octal literals is not supported in 3.x:: \n" 
+                    self.assertIn("using just a '0' prefix for octal literals is not supported in 3.x:: \n"
                                     "use the '0o' prefix for octal integers",
                                     str(oct.exception))
-                              
+
     def test_long_integers(self):
         x = 0L
         x = 0l
@@ -472,7 +472,7 @@ def test_print_py3k_warnings(self):
                 print >> sys.stdout
                 for warning in w:
                     self.assertTrue(Py3xWarning is w.category)
-                    self.assertEqual(str(w.message), "print must be called as a function, not a statement in 3.x", 
+                    self.assertEqual(str(w.message), "print must be called as a function, not a statement in 3.x",
                                      "You can fix this now by using parentheses for arguments to 'print'")
 
     def test_del_stmt(self):
@@ -1057,6 +1057,24 @@ def test_dictcomps(self):
         nums = [1, 2, 3]
         self.assertEqual({i:i+1 for i in nums}, {1: 2, 2: 3, 3: 4})
 
+    def test_listcomp_py3k_paren(self):
+        [x for x in [1, 2, 2]]
+        expected = "list comp without parenthesis is invalid in 3.x: use parenthesis for list items more than one"
+        with check_py3k_warnings((expected, SyntaxWarning)):
+            [x for x in 1, 2, 3]
+
+    def test_listcomps_py3k_scope(self):
+        def foo(): print([x for x in [1, 2, 2]])
+        expected = "This listcomp does not leak a variable in 3.x: assign the variable before use"
+        with check_py3k_warnings((expected, SyntaxWarning)):
+            def foo(): x = 0; [x for x in [1, 2, 2]]; print(x)
+        def foo(): x = 0; print(x); [x for x in [1, 2, 2]]
+        def foo():
+            x = 0
+            if x > 0: 
+                [x for x in [1, 2, 2]]
+                print(x)
+
     def test_listcomps(self):
         # list comprehension tests
         nums = [1, 2, 3, 4, 5]
@@ -1247,7 +1265,7 @@ def test_py3x_unicode_warnings_ur(self):
                 self.assertEqual(ur'foo', u'foo')
                 for warning in w:
                     self.assertTrue(Py3xWarning is w.category)
-                    self.assertEqual(str(w.message), "the 'ur' prefix in string literals is not supported in 3.x: ", 
+                    self.assertEqual(str(w.message), "the 'ur' prefix in string literals is not supported in 3.x: ",
                                      "use a 'u' and two backslashes for a literal backslash")
 
 

Python/ast.c

@@ -903,13 +903,23 @@ ast_for_decorators(struct compiling *c, const node *n)
     return decorator_seq;
 }
 
+static int
+compiler_islistcomp(stmt_ty s)
+{
+    if (s->kind != Expr_kind)
+        return 0;
+    return s->v.Expr.value->kind == ListComp_kind;
+}
+
 static stmt_ty
 ast_for_funcdef(struct compiling *c, const node *n, asdl_seq *decorator_seq)
 {
     /* funcdef: 'def' NAME parameters ':' suite */
     identifier name;
     arguments_ty args;
-    asdl_seq *body;
+    asdl_seq *body, *lstcomp, *var_of_int;
+    int nc, i, y, islistcomp;
+    stmt_ty st, var_st;
     int name_i = 1;
 
     REQ(n, funcdef);
@@ -925,6 +935,26 @@ ast_for_funcdef(struct compiling *c, const node *n, asdl_seq *decorator_seq)
     body = ast_for_suite(c, CHILD(n, name_i + 3));
     if (!body)
         return NULL;
+
+    if (Py_Py3kWarningFlag) {
+        nc = asdl_seq_LEN(body);
+        for (i = 0; i < nc; i++) {
+            st = (stmt_ty)asdl_seq_GET(body, i);
+            islistcomp = compiler_islistcomp(st);
+            if (islistcomp) {
+                lstcomp = asdl_seq_GET(body, i);
+                var_of_int = asdl_seq_GET(lstcomp, 3);
+                for (y=i; y < nc; y++) {
+                    var_st = (stmt_ty)asdl_seq_GET(body, y);
+                    if ((var_st == var_of_int) &&
+                        !ast_3x_warn(c, n, "This listcomp does not leak a variable in 3.x",
+                                     "assign the variable before use"))
+                        return 0;
+                }
+            }
+        }  
+    }
+
 
     return FunctionDef(name, args, body, decorator_seq, LINENO(n),
                        n->n_col_offset, c->c_arena);
@@ -1436,8 +1466,9 @@ ast_for_atom(struct compiling *c, const node *n)
     case LSQB: /* list (or list comprehension) */
         ch = CHILD(n, 1);
 
-        if (TYPE(ch) == RSQB)
+        if (TYPE(ch) == RSQB) {
             return List(NULL, Load, LINENO(n), n->n_col_offset, c->c_arena);
+        }
 
         REQ(ch, listmaker);
         if (NCH(ch) == 1 || TYPE(CHILD(ch, 1)) == COMMA) {
@@ -1448,6 +1479,10 @@ ast_for_atom(struct compiling *c, const node *n)
             return List(elts, Load, LINENO(n), n->n_col_offset, c->c_arena);
         }
         else
+            if (Py_Py3kWarningFlag &&
+                    !ast_3x_warn(c, n, "list comp without parenthesis is invalid in 3.x",
+                            "use parenthesis for list items more than one"))
+                        return NULL;
             return ast_for_listcomp(c, ch);
     case LBRACE: {
         /* dictorsetmaker: