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gh-50720: Set errno and strerror on URLError wrapping an OSError #160938

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Merged
orsenthil merged 2 commits into from
Oct 31, 2026
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gh-50720: Set errno and strerror on URLError wrapping an OSError #160938

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gh-50720: Set errno and strerror on URLError wrapping an OSError
vasiliyk Oct 30, 2026
e10e451
Merge branch 'main' into gh-50720-urllib
orsenthil Oct 31, 2026
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4 changes: 4 additions & 0 deletions Doc/library/urllib.error.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,10 @@ The following exceptions are raised by :mod:`!urllib.error` as appropriate:
:exc:`URLError` used to be a subtype of :exc:`IOError`, which is now an
alias of :exc:`OSError`.

.. versionchanged:: 3.16
The :attr:`~OSError.errno` and :attr:`~OSError.strerror` attributes are
now set from :attr:`reason` when it is an :exc:`OSError`.


.. exception:: HTTPError(url, code, msg, hdrs, fp)

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21 changes: 21 additions & 0 deletions Lib/test/test_urllib2.py
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Expand Up @@ -82,6 +82,27 @@ def test_parse_http_list(self):
def test_URLError_reasonstr(self):
err = urllib.error.URLError('reason')
self.assertIn(err.reason, str(err))
self.assertIsNone(err.errno)
self.assertIsNone(err.strerror)

def test_URLError_OSError_attributes(self):
# gh-50720: errno and strerror are copied from a wrapped OSError.
socket_error = socket.gaierror(-2, 'Name or service not known')

class FailingHTTPConnection(MockHTTPClass):
def request(self, *args, **kwargs):
raise socket_error

h = urllib.request.AbstractHTTPHandler()
req = Request("http://example.com/")
req.timeout = None

with self.assertRaises(urllib.error.URLError) as cm:
h.do_open(FailingHTTPConnection(), req)
err = cm.exception
self.assertIs(err.reason, socket_error)
self.assertEqual(err.errno, -2)
self.assertEqual(err.strerror, 'Name or service not known')


class RequestHdrsTests(unittest.TestCase):
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5 changes: 5 additions & 0 deletions Lib/urllib/error.py
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,11 @@ def __init__(self, reason, filename=None):
self.reason = reason
if filename is not None:
self.filename = filename
if isinstance(reason, OSError):

@orsenthil orsenthil Oct 31, 2026

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The only question is winerror Should we handle that?
We don't have a great on windows and if winerror will be different than errno for the scenarios that URLError will capture.

@orsenthil orsenthil Oct 31, 2026

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Keeping this just as thought. Not a blocker.

@vasiliyk vasiliyk Oct 31, 2026

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Right, winerror stays None on Windows while the wrapped error carries the code. For socket errors it equals errno, but it differs for non-socket errors wrapped by FileHandler.

Should I open a separate improvement issue for it?

@orsenthil orsenthil Oct 31, 2026

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If you have a windows system, could you verify it with a some tests?
Exposing winerror gated by system check will be good.

@vasiliyk vasiliyk Oct 31, 2026

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I only have macOS and Linux.

The CI runs the test suite on Windows, so a Windows-only test would be verified there. I can open a follow-up PR that copies winerror behind a platform check, with the test skipped elsewhere.

What do you think?

@orsenthil orsenthil Oct 31, 2026

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Yes, sounds good to me.

# OSError.__init__() is not called, so copy the attributes
# it would have set from the wrapped error (gh-50720).
self.errno = reason.errno
self.strerror = reason.strerror

def __str__(self):
return '<urlopen error %s>' % self.reason
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Library/2026-10-29-20-52-57.gh-issue-50720.Kd1VMR.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,3 @@
:exc:`urllib.error.URLError` now sets the :attr:`~OSError.errno` and
:attr:`~OSError.strerror` attributes from
:attr:`~urllib.error.URLError.reason` when it is an :exc:`OSError`.
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