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gh-93343: Expand warning filter examples #106618

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gh-93343: Expand warning filter examples
daniel-shimon Jul 12, 2023
f3684a6
gh-93343: Add warning filters tests
daniel-shimon Jul 12, 2023
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28 changes: 28 additions & 0 deletions Doc/library/warnings.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -214,6 +214,34 @@ Some examples::
ignore,default:::mymodule # Only report warnings triggered by "mymodule"
error:::mymodule # Convert warnings to errors in "mymodule"

.. _warning-filter-examples:

Warning Filter Examples
~~~~~~~~~~~~~~~~~~~~~~~

Here are some complex examples for filtering warnings.

Note that :func:`filterwarnings` filters have subtle differences
from :option:`-W` and :envvar:`PYTHONWARNINGS` regarding the *message* and *module*
parts of the filter (as described in :ref:`warning-filter`).

::

filterwarnings("ignore", message=".*generic", module=r"yourmodule\.submodule")
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Suggested change
filterwarnings("ignore", message=".*generic", module=r"yourmodule\.submodule")
filterwarnings("ignore", message="\.*generic", module="yourmodule\.submodule")

Shouldn't this be escaped as well? The r here is not necessary, and its usage should be consistent between the two args (assuming they are both regexes).

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No since the first arg wants to capture strings that contain 'generic' so that the '.' catches everything, while the first arg want to capture 'yourmodule.submodule' specifically, meaning that the '.' actually captures dot and should be escaped

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Well, it sounds to me you should put that explanation into the docs, @daniel-shimon; if it is unclear for a reviewer, it is not going to be clear for the average docs reader ;)

# Ignore warnings in "yourmodule.submodule" which contain "generic"
filterwarnings("ignore", message="generic", module=r"yourmodule\.submodule")
# Ignore warnings in "yourmodule.submodule" which START with "generic"
filterwarnings("ignore", module="yourmodule.*")
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filterwarnings("ignore", module="yourmodule.*")
filterwarnings("ignore", module="yourmodule\.*")

I think this should be escaped too.

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@erlend-aasland erlend-aasland Jul 11, 2023 •
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Also, instead of using comments, would it be clearer (formatting wise) to use multiple code blocks? (Goes for the change below as well)

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No because here we actually want to catch all characters after 'yourmodule' and not only dot

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Ditto: https://github.com/python/cpython/pull/106618/files#r1261710032

# Ignore all warnings in "yourmodule" and its submodules

-W "ignore:generic::yourmodule.submodule:"
# Ignore warnings in "yourmodule.submodule" which START with "generic"
# (but not those containing it).
# Also note that the '.' in the module does not need to be escaped
# since it is not a regex.
-W "ignore:::yourmodule:"
# Ignore all warnings in "yourmodule", but NOT in its submodules


.. _default-warning-filter:

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24 changes: 24 additions & 0 deletions Lib/test/test_warnings/__init__.py
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Expand Up @@ -312,6 +312,18 @@ def test_message_matching(self):
self.module.warn("something completely different")
self.assertEqual(w, [])

def test_message_matching_regex(self):
with original_warnings.catch_warnings(record=True,
module=self.module) as w:
self.module.simplefilter("ignore", UserWarning)
self.module.filterwarnings("error", ".*match", UserWarning)
self.assertRaises(UserWarning, self.module.warn, "match")
self.assertRaises(UserWarning, self.module.warn, "match prefix")
self.assertRaises(UserWarning, self.module.warn, "suffix match")
self.assertEqual(w, [])
self.module.warn("not a m4tch")
self.assertEqual(w, [])

def test_mutate_filter_list(self):
class X:
def match(self, a):
Expand Down Expand Up @@ -1202,6 +1214,18 @@ def test_single_warning(self):
PYTHONDEVMODE="")
self.assertEqual(stdout, b"['ignore::DeprecationWarning']")

def test_string_literals(self):
# Ensure message/module are treated as string literals
rc, stdout, stderr = assert_python_ok("-c",
"import sys, warnings; "
"sys.stdout.write(warnings.filters[0][1].pattern); "
"sys.stderr.write(warnings.filters[0][3].pattern)",
PYTHONWARNINGS="ignore:.generic::yourmodule.submodule",
PYTHONDEVMODE="")
self.assertEqual(stdout, rb"\.generic")
# '\Z' is added to the module name, so check start of pattern:
self.assertTrue(stderr.startswith(rb"yourmodule\.submodule"))

def test_comma_separated_warnings(self):
rc, stdout, stderr = assert_python_ok("-c",
"import sys; sys.stdout.write(str(sys.warnoptions))",
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2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Documentation/2023-07-11-08-46-13.gh-issue-93343.fw_eyw.rst
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@@ -0,0 +1,2 @@
Add examples of warning filters and the difference between programmatic and
environmental filters.
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