https://github.com/python/cpython/commit/47d2f68df215b5bcbc76a50d3f4e0b68791e3e79
commit: 47d2f68df215b5bcbc76a50d3f4e0b68791e3e79
branch: main
author: Stan Ulbrych <[email protected]>
committer: encukou <[email protected]>
date: 2025-10-21T09:12:04+02:00
summary:
gh-139707: Better `ModuleNotFoundError` message for missing stdlib modules
(GH-140219)
files:
A Misc/NEWS.d/next/Library/2025-10-16-16-10-11.gh-issue-139707.zR6Qtn.rst
M Lib/test/test_traceback.py
M Lib/traceback.py
diff --git a/Lib/test/test_traceback.py b/Lib/test/test_traceback.py
index bd3ecfd9a3863d..bf57867a8715c0 100644
--- a/Lib/test/test_traceback.py
+++ b/Lib/test/test_traceback.py
@@ -5034,7 +5034,8 @@ def test_no_site_package_flavour(self):
self.assertIn(
(b"Site initialization is disabled, did you forget to "
- b"add the site-packages directory to sys.path?"), stderr
+ b"add the site-packages directory to sys.path "
+ b"or to enable your virtual environment?"), stderr
)
code = """
@@ -5046,9 +5047,20 @@ def test_no_site_package_flavour(self):
self.assertNotIn(
(b"Site initialization is disabled, did you forget to "
- b"add the site-packages directory to sys.path?"), stderr
+ b"add the site-packages directory to sys.path "
+ b"or to enable your virtual environment?"), stderr
)
+ def test_missing_stdlib_package(self):
+ code = """
+ import sys
+ sys.stdlib_module_names |= {'spam'}
+ import spam
+ """
+ _, _, stderr = assert_python_failure('-S', '-c', code)
+
+ self.assertIn(b"Standard library module 'spam' was not found", stderr)
+
class TestColorizedTraceback(unittest.TestCase):
maxDiff = None
diff --git a/Lib/traceback.py b/Lib/traceback.py
index 692d44837936ee..9b4b8c7d566fe8 100644
--- a/Lib/traceback.py
+++ b/Lib/traceback.py
@@ -1107,11 +1107,14 @@ def __init__(self, exc_type, exc_value, exc_traceback,
*, limit=None,
suggestion = _compute_suggestion_error(exc_value, exc_traceback,
wrong_name)
if suggestion:
self._str += f". Did you mean: '{suggestion}'?"
- elif exc_type and issubclass(exc_type, ModuleNotFoundError) and \
- sys.flags.no_site and \
- getattr(exc_value, "name", None) not in
sys.stdlib_module_names:
- self._str += (". Site initialization is disabled, did you forget
to "
- + "add the site-packages directory to sys.path?")
+ elif exc_type and issubclass(exc_type, ModuleNotFoundError):
+ module_name = getattr(exc_value, "name", None)
+ if module_name in sys.stdlib_module_names:
+ self._str = f"Standard library module '{module_name}' was not
found"
+ elif sys.flags.no_site:
+ self._str += (". Site initialization is disabled, did you
forget to "
+ + "add the site-packages directory to sys.path "
+ + "or to enable your virtual environment?")
elif exc_type and issubclass(exc_type, (NameError, AttributeError))
and \
getattr(exc_value, "name", None) is not None:
wrong_name = getattr(exc_value, "name", None)
diff --git
a/Misc/NEWS.d/next/Library/2025-10-16-16-10-11.gh-issue-139707.zR6Qtn.rst
b/Misc/NEWS.d/next/Library/2025-10-16-16-10-11.gh-issue-139707.zR6Qtn.rst
new file mode 100644
index 00000000000000..c5460aae8b3638
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-10-16-16-10-11.gh-issue-139707.zR6Qtn.rst
@@ -0,0 +1,2 @@
+Improve :exc:`ModuleNotFoundError` error message when a :term:`standard
library`
+module is missing.
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