check by equality for __future__ not identity (closes #14378)

Lib/test/test_ast.py

@@ -231,6 +231,12 @@ class AST_Tests(unittest.TestCase):
         im = ast.parse("from . import y").body[0]
         self.assertIsNone(im.module)
 
+    def test_non_interned_future_from_ast(self):
+        mod = ast.parse("from __future__ import division")
+        self.assertIsInstance(mod.body[0], ast.ImportFrom)
+        mod.body[0].module = " __future__ ".strip()
+        compile(mod, "<test>", "exec")
+
     def test_base_classes(self):
         self.assertTrue(issubclass(ast.For, ast.stmt))
         self.assertTrue(issubclass(ast.Name, ast.expr))

Misc/NEWS

@@ -9,6 +9,9 @@ What's New in Python 2.7.4
 Core and Builtins
 -----------------
 
+- Issue #14378: Fix compiling ast.ImportFrom nodes with a "__future__" string as
+  the module name that was not interned.
+
 - Issue #14331: Use significantly less stack space when importing modules by
   allocating path buffers on the heap instead of the stack.
 

Python/future.c

@@ -59,13 +59,6 @@ future_parse(PyFutureFeatures *ff, mod_ty mod, const char *filename)
 {
     int i, found_docstring = 0, done = 0, prev_line = 0;
 
-    static PyObject *future;
-    if (!future) {
-        future = PyString_InternFromString("__future__");
-        if (!future)
-            return 0;
-    }
-
     if (!(mod->kind == Module_kind || mod->kind == Interactive_kind))
         return 1;
 
@@ -92,7 +85,9 @@ future_parse(PyFutureFeatures *ff, mod_ty mod, const char *filename)
         */
 
         if (s->kind == ImportFrom_kind) {
-            if (s->v.ImportFrom.module == future) {
+            PyObject *modname = s->v.ImportFrom.module;
+            if (PyString_GET_SIZE(modname) == 10 &&
+                !strcmp(PyString_AS_STRING(modname), "__future__")) {
                 if (done) {
                     PyErr_SetString(PyExc_SyntaxError,
                                     ERR_LATE_FUTURE);