bpo-29546: Improve from-import error message with location (#103)

bpo-29546: Improve from-import error message with location

1 files changed, 21 insertions, 4 deletions

diff --git a/Python/ceval.c b/Python/ceval.c
index 69c9383..81c89df 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -4995,7 +4995,7 @@ import_from(PyObject *v, PyObject *name)
 {
     PyObject *x;
     _Py_IDENTIFIER(__name__);
-    PyObject *fullmodname, *pkgname, *pkgpath;
+    PyObject *fullmodname, *pkgname, *pkgpath, *pkgname_or_unknown;
 
     x = PyObject_GetAttr(v, name);
     if (x != NULL || !PyErr_ExceptionMatches(PyExc_AttributeError))
@@ -5009,7 +5009,6 @@ import_from(PyObject *v, PyObject *name)
         goto error;
     }
     fullmodname = PyUnicode_FromFormat("%U.%U", pkgname, name);
-    Py_DECREF(pkgname);
     if (fullmodname == NULL) {
         return NULL;
     }
@@ -5018,18 +5017,36 @@ import_from(PyObject *v, PyObject *name)
     if (x == NULL) {
         goto error;
     }
+    Py_DECREF(pkgname);
     Py_INCREF(x);
     return x;
  error:
     pkgpath = PyModule_GetFilenameObject(v);
+    if (pkgname == NULL) {
+        pkgname_or_unknown = PyUnicode_FromString("<unknown module name>");
+        if (pkgname_or_unknown == NULL) {
+            Py_XDECREF(pkgpath);
+            return NULL;
+        }
+    } else {
+        pkgname_or_unknown = pkgname;
+    }
 
     if (pkgpath == NULL || !PyUnicode_Check(pkgpath)) {
         PyErr_Clear();
-        PyErr_SetImportError(PyUnicode_FromFormat("cannot import name %R", name), pkgname, NULL);
+        PyErr_SetImportError(
+            PyUnicode_FromFormat("cannot import name %R from %R (unknown location)",
+                name, pkgname_or_unknown),
+            pkgname, NULL);
     } else {
-        PyErr_SetImportError(PyUnicode_FromFormat("cannot import name %R", name), pkgname, pkgpath);
+        PyErr_SetImportError(
+            PyUnicode_FromFormat("cannot import name %R from %R (%S)",
+                name, pkgname_or_unknown, pkgpath),
+            pkgname, pkgpath);
     }
 
+    Py_XDECREF(pkgname_or_unknown);
+    Py_XDECREF(pkgpath);
     return NULL;
 }