bpo-20490: Improve circular import error message (GH-15308)
diff --git a/Lib/test/test_import/__init__.py b/Lib/test/test_import/__init__.py
index 50406d9..7c24f0e 100644
--- a/Lib/test/test_import/__init__.py
+++ b/Lib/test/test_import/__init__.py
@@ -1326,6 +1326,16 @@
self.assertIn('partially initialized module', errmsg)
self.assertIn('circular import', errmsg)
+ def test_circular_from_import(self):
+ with self.assertRaises(ImportError) as cm:
+ import test.test_import.data.circular_imports.from_cycle1
+ self.assertIn(
+ "cannot import name 'b' from partially initialized module "
+ "'test.test_import.data.circular_imports.from_cycle1' "
+ "(most likely due to a circular import)",
+ str(cm.exception),
+ )
+
if __name__ == '__main__':
# Test needs to be a package, so we can do relative imports.
diff --git a/Lib/test/test_import/data/circular_imports/from_cycle1.py b/Lib/test/test_import/data/circular_imports/from_cycle1.py
new file mode 100644
index 0000000..aacfd5f
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/from_cycle1.py
@@ -0,0 +1,2 @@
+from .from_cycle2 import a
+b = 1
diff --git a/Lib/test/test_import/data/circular_imports/from_cycle2.py b/Lib/test/test_import/data/circular_imports/from_cycle2.py
new file mode 100644
index 0000000..62a66e1
--- /dev/null
+++ b/Lib/test/test_import/data/circular_imports/from_cycle2.py
@@ -0,0 +1,2 @@
+from .from_cycle1 import b
+a = 1
diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-08-15-12-48-36.bpo-20490.-hXeEn.rst b/Misc/NEWS.d/next/Core and Builtins/2019-08-15-12-48-36.bpo-20490.-hXeEn.rst
new file mode 100644
index 0000000..dfee480
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-08-15-12-48-36.bpo-20490.-hXeEn.rst
@@ -0,0 +1,2 @@
+Improve import error message for partially initialized module on circular
+``from`` imports - by Anthony Sottile.
diff --git a/Python/ceval.c b/Python/ceval.c
index 546a426..07ec329 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -5236,10 +5236,17 @@
PyErr_SetImportError(errmsg, pkgname, NULL);
}
else {
- errmsg = PyUnicode_FromFormat(
- "cannot import name %R from %R (%S)",
- name, pkgname_or_unknown, pkgpath
- );
+ _Py_IDENTIFIER(__spec__);
+ PyObject *spec = _PyObject_GetAttrId(v, &PyId___spec__);
+ Py_XINCREF(spec);
+ const char *fmt =
+ _PyModuleSpec_IsInitializing(spec) ?
+ "cannot import name %R from partially initialized module %R "
+ "(most likely due to a circular import) (%S)" :
+ "cannot import name %R from %R (%S)";
+ Py_XDECREF(spec);
+
+ errmsg = PyUnicode_FromFormat(fmt, name, pkgname_or_unknown, pkgpath);
/* NULL checks for errmsg and pkgname done by PyErr_SetImportError. */
PyErr_SetImportError(errmsg, pkgname, pkgpath);
}