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

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

Author: Carreau

Doc/whatsnew/3.7.rst

@@ -83,6 +83,9 @@ Other Language Changes
  whitespace, not only spaces.
  (Contributed by Robert Xiao in :issue:`28927`.)
 
+* :exc:`ImportError` now displays module name and module ``__file__`` path when
+ ``from ... import ...`` fails. :issue:`29546`.
+
 
 New Modules
 ===========

Lib/test/test_import/__init__.py

@@ -85,6 +85,15 @@ def test_from_import_missing_attr_has_name_and_path(self):
  from os import i_dont_exist
  self.assertEqual(cm.exception.name, 'os')
  self.assertEqual(cm.exception.path, os.__file__)
+ self.assertRegex(str(cm.exception), "cannot import name 'i_dont_exist' from 'os' \(.*/Lib/os.py\)")
+
+ def test_from_import_missing_attr_has_name_and_so_path(self):
+ import _opcode
+ with self.assertRaises(ImportError) as cm:
+ from _opcode import i_dont_exist
+ self.assertEqual(cm.exception.name, '_opcode')
+ self.assertEqual(cm.exception.path, _opcode.__file__)
+ self.assertRegex(str(cm.exception), "cannot import name 'i_dont_exist' from '_opcode' \(.*\.(so|dll)\)")
 
  def test_from_import_missing_attr_has_name(self):
  with self.assertRaises(ImportError) as cm:
@@ -365,9 +374,12 @@ def __getattr__(self, _):
  module_name = 'test_from_import_AttributeError'
  self.addCleanup(unload, module_name)
  sys.modules[module_name] = AlwaysAttributeError()
- with self.assertRaises(ImportError):
+ with self.assertRaises(ImportError) as cm:
  from test_from_import_AttributeError import does_not_exist
 
+ self.assertEqual(str(cm.exception),
+ "cannot import name 'does_not_exist' from '<unknown module name>' (unknown location)")
+
 
 @skip_if_dont_write_bytecode
 class FilePermissionTests(unittest.TestCase):

Misc/NEWS

@@ -24,6 +24,8 @@ Core and Builtins
 
 - bpo-29546: Set the 'path' and 'name' attribute on ImportError for ``from ... import ...``.
 
+- bpo-29546: Improve from-import error message with location
+
 - Issue #29319: Prevent RunMainFromImporter overwriting sys.path[0].
 
 - Issue #29337: Fixed possible BytesWarning when compare the code objects.

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;
 }