Issue #18018: Raise an ImportError if a relative import is attempted

brettcannon · brettcannon · commit 9fa812668faf · 2016-01-22T16:39:02.000-08:00
with no known parent package.

Previously SystemError was raised if the parent package didn't exist
(e.g., __package__ was set to '').
Thanks to Florent Xicluna and Yongzhi Pan for reporting the issue.
diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst
@@ -278,6 +278,10 @@ Changes in the Python API
   to ``__spec__.parent`` then :exc:`ImportWarning` is raised.
   (Contributed by Brett Cannon in :issue:`25791`.)
 
+* When a relative import is performed and no parent package is known, then
+  :exc:`ImportError` will be raised. Previously, :exc:`SystemError` could be
+  raised. (Contribute by Brett Cannon in :issue:`18018`.)
+
 
 Changes in the C API
 --------------------
diff --git a/Lib/test/test_importlib/import_/test_relative_imports.py b/Lib/test/test_importlib/import_/test_relative_imports.py
@@ -213,6 +213,11 @@ def test_relative_import_no_globals(self):
             with self.assertRaises(KeyError):
                 self.__import__('sys', level=1)
 
+    def test_relative_import_no_package(self):
+        with self.assertRaises(ImportError):
+            self.__import__('a', {'__package__': '', '__spec__': None},
+                            level=1)
+
 
 (Frozen_RelativeImports,
  Source_RelativeImports
diff --git a/Misc/NEWS b/Misc/NEWS
@@ -10,6 +10,9 @@ Release date: tba
 Core and Builtins
 -----------------
 
+- Issue #18018: Import raises ImportError instead of SystemError if a relative
+  import is attempted without a known parent package.
+
 - Issue #25843: When compiling code, don't merge constants if they are equal
   but have a different types. For example, ``f1, f2 = lambda: 1, lambda: 1.0``
   is now correctly compiled to two different functions: ``f1()`` returns ``1``
diff --git a/Python/import.c b/Python/import.c
@@ -1424,7 +1424,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *given_globals,
                 PyErr_SetString(PyExc_TypeError, "package must be a string");
                 goto error;
             }
-            else if (spec != NULL) {
+            else if (spec != NULL && spec != Py_None) {
                 int equal;
                 PyObject *parent = PyObject_GetAttrString(spec, "parent");
                 if (parent == NULL) {
@@ -1444,7 +1444,7 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *given_globals,
                 }
             }
         }
-        else if (spec != NULL) {
+        else if (spec != NULL && spec != Py_None) {
             package = PyObject_GetAttrString(spec, "parent");
             if (package == NULL) {
                 goto error;
@@ -1491,7 +1491,12 @@ PyImport_ImportModuleLevelObject(PyObject *name, PyObject *given_globals,
             }
         }
 
-        if (PyDict_GetItem(interp->modules, package) == NULL) {
+        if (PyUnicode_CompareWithASCIIString(package, "") == 0) {
+            PyErr_SetString(PyExc_ImportError,
+                    "attempted relative import with no known parent package");
+            goto error;
+        }
+        else if (PyDict_GetItem(interp->modules, package) == NULL) {
             PyErr_Format(PyExc_SystemError,
                     "Parent module %R not loaded, cannot perform relative "
                     "import", package);

Original file line number	Diff line number	Diff line change
`@@ -1424,7 +1424,7 @@ PyImport_ImportModuleLevelObject(PyObject name, PyObject given_globals,`
`1424`	`1424`	`PyErr_SetString(PyExc_TypeError, "package must be a string");`
`1425`	`1425`	`goto error;`
`1426`	`1426`	`}`
`1427`		`- else if (spec != NULL) {`
	`1427`	`+ else if (spec != NULL && spec != Py_None) {`
`1428`	`1428`	`int equal;`
`1429`	`1429`	`PyObject *parent = PyObject_GetAttrString(spec, "parent");`
`1430`	`1430`	`if (parent == NULL) {`
`@@ -1444,7 +1444,7 @@ PyImport_ImportModuleLevelObject(PyObject name, PyObject given_globals,`
`1444`	`1444`	`}`
`1445`	`1445`	`}`
`1446`	`1446`	`}`
`1447`		`- else if (spec != NULL) {`
	`1447`	`+ else if (spec != NULL && spec != Py_None) {`
`1448`	`1448`	`package = PyObject_GetAttrString(spec, "parent");`
`1449`	`1449`	`if (package == NULL) {`
`1450`	`1450`	`goto error;`
`@@ -1491,7 +1491,12 @@ PyImport_ImportModuleLevelObject(PyObject name, PyObject given_globals,`
`1491`	`1491`	`}`
`1492`	`1492`	`}`
`1493`	`1493`
`1494`		`- if (PyDict_GetItem(interp->modules, package) == NULL) {`
	`1494`	`+ if (PyUnicode_CompareWithASCIIString(package, "") == 0) {`
	`1495`	`+ PyErr_SetString(PyExc_ImportError,`
	`1496`	`+ "attempted relative import with no known parent package");`
	`1497`	`+ goto error;`
	`1498`	`+ }`
	`1499`	`+ else if (PyDict_GetItem(interp->modules, package) == NULL) {`
`1495`	`1500`	`PyErr_Format(PyExc_SystemError,`
`1496`	`1501`	`"Parent module %R not loaded, cannot perform relative "`
`1497`	`1502`	`"import", package);`