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bpo-20490: Improve circular import error messaging #15308

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Merged
merged 1 commit into from
Sep 9, 2019
Merged

bpo-20490: Improve circular import error messaging #15308

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10 changes: 10 additions & 0 deletions Lib/test/test_import/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1324,6 +1324,16 @@ def test_crossreference2(self):
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.
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2 changes: 2 additions & 0 deletions Lib/test/test_import/data/circular_imports/from_cycle1.py
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@@ -0,0 +1,2 @@
from .from_cycle2 import a
b = 1
2 changes: 2 additions & 0 deletions Lib/test/test_import/data/circular_imports/from_cycle2.py
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@@ -0,0 +1,2 @@
from .from_cycle1 import b
a = 1
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-08-15-12-48-36.bpo-20490.-hXeEn.rst
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@@ -0,0 +1,2 @@
Improve import error message for partially initialized module on circular
``from`` imports - by Anthony Sottile.
15 changes: 11 additions & 4 deletions Python/ceval.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5238,10 +5238,17 @@ import_from(PyThreadState *tstate, PyObject *v, PyObject *name)
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);
}
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