FM / library

/usr/share/doc/python3-docs/html/_sources/library/

/usr/share/doc/python3-docs/html/_sources/library

Name	Size	Mode	Actions
2to3.rst.txt	15898	0644	edit dl rm
abc.rst.txt	11805	0644	edit dl rm
aifc.rst.txt	7503	0644	edit dl rm
allos.rst.txt	678	0644	edit dl rm
archiving.rst.txt	440	0644	edit dl rm
argparse.rst.txt	77480	0644	edit dl rm
array.rst.txt	10812	0644	edit dl rm
ast.rst.txt	10159	0644	edit dl rm
asynchat.rst.txt	8528	0644	edit dl rm
asyncio-dev.rst.txt	13398	0644	edit dl rm
asyncio-eventloop.rst.txt	33701	0644	edit dl rm
asyncio-eventloops.rst.txt	7660	0644	edit dl rm
asyncio-protocol.rst.txt	25170	0644	edit dl rm
asyncio-queue.rst.txt	4328	0644	edit dl rm
asyncio-stream.rst.txt	14363	0644	edit dl rm
asyncio-subprocess.rst.txt	15544	0644	edit dl rm
asyncio-sync.rst.txt	9078	0644	edit dl rm
asyncio-task.rst.txt	25406	0644	edit dl rm
asyncio.rst.txt	2272	0644	edit dl rm
asyncore.rst.txt	13624	0644	edit dl rm
atexit.rst.txt	3669	0644	edit dl rm
audioop.rst.txt	10712	0644	edit dl rm
base64.rst.txt	10371	0644	edit dl rm
bdb.rst.txt	12985	0644	edit dl rm
binary.rst.txt	654	0644	edit dl rm
binascii.rst.txt	6539	0644	edit dl rm
binhex.rst.txt	1709	0644	edit dl rm
bisect.rst.txt	5398	0644	edit dl rm
builtins.rst.txt	1465	0644	edit dl rm
bz2.rst.txt	8825	0644	edit dl rm
calendar.rst.txt	10988	0644	edit dl rm
cgi.rst.txt	22650	0644	edit dl rm
cgitb.rst.txt	2918	0644	edit dl rm
chunk.rst.txt	5094	0644	edit dl rm
cmath.rst.txt	9326	0644	edit dl rm
cmd.rst.txt	13795	0644	edit dl rm
code.rst.txt	7817	0644	edit dl rm
codecs.rst.txt	75564	0644	edit dl rm
codeop.rst.txt	3021	0644	edit dl rm
collections.abc.rst.txt	12861	0644	edit dl rm
collections.rst.txt	46063	0644	edit dl rm
colorsys.rst.txt	1820	0644	edit dl rm
compileall.rst.txt	8975	0644	edit dl rm
concurrency.rst.txt	673	0644	edit dl rm
concurrent.futures.rst.txt	16910	0644	edit dl rm
concurrent.rst.txt	171	0644	edit dl rm
configparser.rst.txt	48756	0644	edit dl rm
constants.rst.txt	3331	0644	edit dl rm
contextlib.rst.txt	28175	0644	edit dl rm
copy.rst.txt	3378	0644	edit dl rm
copyreg.rst.txt	2182	0644	edit dl rm
crypt.rst.txt	5122	0644	edit dl rm
crypto.rst.txt	411	0644	edit dl rm
csv.rst.txt	19902	0644	edit dl rm
ctypes.rst.txt	88613	0644	edit dl rm
curses.ascii.rst.txt	8920	0644	edit dl rm
curses.panel.rst.txt	2764	0644	edit dl rm
curses.rst.txt	76397	0644	edit dl rm
custominterp.rst.txt	569	0644	edit dl rm
datatypes.rst.txt	751	0644	edit dl rm
datetime.rst.txt	90524	0644	edit dl rm
dbm.rst.txt	14293	0644	edit dl rm
debug.rst.txt	471	0644	edit dl rm
decimal.rst.txt	74869	0644	edit dl rm
development.rst.txt	704	0644	edit dl rm
difflib.rst.txt	29861	0644	edit dl rm
dis.rst.txt	32567	0644	edit dl rm
distribution.rst.txt	452	0644	edit dl rm
distutils.rst.txt	1974	0644	edit dl rm
doctest.rst.txt	71743	0644	edit dl rm
dummy_threading.rst.txt	784	0644	edit dl rm
email.charset.rst.txt	9293	0644	edit dl rm
email.compat32-message.rst.txt	33493	0644	edit dl rm
email.contentmanager.rst.txt	9112	0644	edit dl rm
email.encoders.rst.txt	2715	0644	edit dl rm
email.errors.rst.txt	4792	0644	edit dl rm
email.examples.rst.txt	1915	0644	edit dl rm
email.generator.rst.txt	13637	0644	edit dl rm
email.header.rst.txt	9188	0644	edit dl rm
email.headerregistry.rst.txt	17957	0644	edit dl rm
email.iterators.rst.txt	2795	0644	edit dl rm
email.message.rst.txt	33008	0644	edit dl rm
email.mime.rst.txt	11721	0644	edit dl rm
email.parser.rst.txt	14092	0644	edit dl rm
email.policy.rst.txt	27022	0644	edit dl rm
email.rst.txt	6785	0644	edit dl rm
email.util.rst.txt	9214	0644	edit dl rm
ensurepip.rst.txt	4987	0644	edit dl rm
enum.rst.txt	32751	0644	edit dl rm
errno.rst.txt	6811	0644	edit dl rm
exceptions.rst.txt	25570	0644	edit dl rm
faulthandler.rst.txt	6136	0644	edit dl rm
fcntl.rst.txt	7152	0644	edit dl rm
filecmp.rst.txt	5623	0644	edit dl rm
fileformats.rst.txt	287	0644	edit dl rm
fileinput.rst.txt	8051	0644	edit dl rm
filesys.rst.txt	961	0644	edit dl rm
fnmatch.rst.txt	3103	0644	edit dl rm
formatter.rst.txt	13242	0644	edit dl rm
fpectl.rst.txt	4180	0644	edit dl rm
fractions.rst.txt	6364	0644	edit dl rm
frameworks.rst.txt	391	0644	edit dl rm
ftplib.rst.txt	17552	0644	edit dl rm
functional.rst.txt	365	0644	edit dl rm
functions.rst.txt	71621	0644	edit dl rm
functools.rst.txt	18503	0644	edit dl rm
gc.rst.txt	9694	0644	edit dl rm
getopt.rst.txt	6557	0644	edit dl rm
getpass.rst.txt	1882	0644	edit dl rm
gettext.rst.txt	25588	0644	edit dl rm
glob.rst.txt	3508	0644	edit dl rm
grp.rst.txt	2417	0644	edit dl rm
gzip.rst.txt	8301	0644	edit dl rm
hashlib.rst.txt	26523	0644	edit dl rm
heapq.rst.txt	13402	0644	edit dl rm
hmac.rst.txt	4020	0644	edit dl rm
html.entities.rst.txt	1319	0644	edit dl rm
html.parser.rst.txt	11275	0644	edit dl rm
html.rst.txt	1304	0644	edit dl rm
http.client.rst.txt	18870	0644	edit dl rm
http.cookiejar.rst.txt	27832	0644	edit dl rm
http.cookies.rst.txt	8645	0644	edit dl rm
http.rst.txt	7096	0644	edit dl rm
http.server.rst.txt	17639	0644	edit dl rm
i18n.rst.txt	408	0644	edit dl rm
idle.rst.txt	25834	0644	edit dl rm
imaplib.rst.txt	20367	0644	edit dl rm
imghdr.rst.txt	2938	0644	edit dl rm
imp.rst.txt	15548	0644	edit dl rm
importlib.rst.txt	53563	0644	edit dl rm
index.rst.txt	2258	0644	edit dl rm
inspect.rst.txt	53928	0644	edit dl rm
internet.rst.txt	992	0644	edit dl rm
intro.rst.txt	2645	0644	edit dl rm
io.rst.txt	40328	0644	edit dl rm
ipaddress.rst.txt	32340	0644	edit dl rm
ipc.rst.txt	649	0644	edit dl rm
itertools.rst.txt	38459	0644	edit dl rm
json.rst.txt	27876	0644	edit dl rm
keyword.rst.txt	617	0644	edit dl rm
language.rst.txt	522	0644	edit dl rm
linecache.rst.txt	2408	0644	edit dl rm
locale.rst.txt	25470	0644	edit dl rm
logging.config.rst.txt	33886	0644	edit dl rm
logging.handlers.rst.txt	42497	0644	edit dl rm
logging.rst.txt	60479	0644	edit dl rm
lzma.rst.txt	17361	0644	edit dl rm
macpath.rst.txt	707	0644	edit dl rm
mailbox.rst.txt	63055	0644	edit dl rm
mailcap.rst.txt	3691	0644	edit dl rm
markup.rst.txt	679	0644	edit dl rm
marshal.rst.txt	4855	0644	edit dl rm
math.rst.txt	14375	0644	edit dl rm
mimetypes.rst.txt	9839	0644	edit dl rm
misc.rst.txt	247	0644	edit dl rm
mm.rst.txt	431	0644	edit dl rm
mmap.rst.txt	11232	0644	edit dl rm
modulefinder.rst.txt	3240	0644	edit dl rm
modules.rst.txt	355	0644	edit dl rm
msilib.rst.txt	18612	0644	edit dl rm
msvcrt.rst.txt	4392	0644	edit dl rm
multiprocessing.rst.txt	104494	0644	edit dl rm
netdata.rst.txt	339	0644	edit dl rm
netrc.rst.txt	3007	0644	edit dl rm
nis.rst.txt	1993	0644	edit dl rm
nntplib.rst.txt	21821	0644	edit dl rm
numbers.rst.txt	8089	0644	edit dl rm
numeric.rst.txt	696	0644	edit dl rm
operator.rst.txt	18989	0644	edit dl rm
optparse.rst.txt	76996	0644	edit dl rm
os.path.rst.txt	16419	0644	edit dl rm
os.rst.txt	137534	0644	edit dl rm
ossaudiodev.rst.txt	17845	0644	edit dl rm
othergui.rst.txt	2822	0644	edit dl rm
parser.rst.txt	15148	0644	edit dl rm
pathlib.rst.txt	30045	0644	edit dl rm
pdb.rst.txt	19454	0644	edit dl rm
persistence.rst.txt	591	0644	edit dl rm
pickle.rst.txt	37440	0644	edit dl rm
pickletools.rst.txt	3729	0644	edit dl rm
pipes.rst.txt	2557	0644	edit dl rm
pkgutil.rst.txt	8730	0644	edit dl rm
platform.rst.txt	9624	0644	edit dl rm
plistlib.rst.txt	7398	0644	edit dl rm
poplib.rst.txt	8197	0644	edit dl rm
posix.rst.txt	3694	0644	edit dl rm
pprint.rst.txt	14274	0644	edit dl rm
profile.rst.txt	27969	0644	edit dl rm
pty.rst.txt	3123	0644	edit dl rm
pwd.rst.txt	2739	0644	edit dl rm
pyclbr.rst.txt	3297	0644	edit dl rm
pydoc.rst.txt	4688	0644	edit dl rm
pyexpat.rst.txt	28620	0644	edit dl rm
python.rst.txt	475	0644	edit dl rm
py_compile.rst.txt	3851	0644	edit dl rm
queue.rst.txt	7268	0644	edit dl rm
quopri.rst.txt	2571	0644	edit dl rm
random.rst.txt	18503	0644	edit dl rm
re.rst.txt	64936	0644	edit dl rm
readline.rst.txt	11943	0644	edit dl rm
reprlib.rst.txt	5162	0644	edit dl rm
resource.rst.txt	12291	0644	edit dl rm
rlcompleter.rst.txt	2294	0644	edit dl rm
runpy.rst.txt	8285	0644	edit dl rm
sched.rst.txt	4842	0644	edit dl rm
secrets.rst.txt	5930	0644	edit dl rm
select.rst.txt	28175	0644	edit dl rm
selectors.rst.txt	8925	0644	edit dl rm
shelve.rst.txt	8390	0644	edit dl rm
shlex.rst.txt	16441	0644	edit dl rm
shutil.rst.txt	26014	0644	edit dl rm
signal.rst.txt	17218	0644	edit dl rm
site.rst.txt	9628	0644	edit dl rm
smtpd.rst.txt	10806	0644	edit dl rm
smtplib.rst.txt	23439	0644	edit dl rm
sndhdr.rst.txt	1994	0644	edit dl rm
socket.rst.txt	68202	0644	edit dl rm
socketserver.rst.txt	23712	0644	edit dl rm
spwd.rst.txt	2958	0644	edit dl rm
sqlite3.rst.txt	39215	0644	edit dl rm
ssl.rst.txt	96021	0644	edit dl rm
stat.rst.txt	9805	0644	edit dl rm
statistics.rst.txt	15301	0644	edit dl rm
stdtypes.rst.txt	179240	0644	edit dl rm
string.rst.txt	35374	0644	edit dl rm
stringprep.rst.txt	4279	0644	edit dl rm
struct.rst.txt	19581	0644	edit dl rm
subprocess.rst.txt	45793	0644	edit dl rm
sunau.rst.txt	7390	0644	edit dl rm
superseded.rst.txt	258	0644	edit dl rm
symbol.rst.txt	975	0644	edit dl rm
symtable.rst.txt	4964	0644	edit dl rm
sys.rst.txt	58273	0644	edit dl rm
sysconfig.rst.txt	8749	0644	edit dl rm
syslog.rst.txt	4302	0644	edit dl rm
tabnanny.rst.txt	2007	0644	edit dl rm
tarfile.rst.txt	31749	0644	edit dl rm
telnetlib.rst.txt	7899	0644	edit dl rm
tempfile.rst.txt	13857	0644	edit dl rm
termios.rst.txt	3751	0644	edit dl rm
test.rst.txt	25764	0644	edit dl rm
text.rst.txt	584	0644	edit dl rm
textwrap.rst.txt	10519	0644	edit dl rm
threading.rst.txt	39257	0644	edit dl rm
time.rst.txt	32967	0644	edit dl rm
timeit.rst.txt	13000	0644	edit dl rm
tk.rst.txt	1639	0644	edit dl rm
tkinter.rst.txt	33027	0644	edit dl rm
tkinter.scrolledtext.rst.txt	1255	0644	edit dl rm
tkinter.tix.rst.txt	22653	0644	edit dl rm
tkinter.ttk.rst.txt	58489	0644	edit dl rm
token.rst.txt	2607	0644	edit dl rm
tokenize.rst.txt	10002	0644	edit dl rm
trace.rst.txt	6914	0644	edit dl rm
traceback.rst.txt	17854	0644	edit dl rm
tracemalloc.rst.txt	22089	0644	edit dl rm
tty.rst.txt	1097	0644	edit dl rm
turtle.rst.txt	71221	0644	edit dl rm
types.rst.txt	9999	0644	edit dl rm
typing.rst.txt	34332	0644	edit dl rm
undoc.rst.txt	780	0644	edit dl rm
unicodedata.rst.txt	5762	0644	edit dl rm
unittest.mock-examples.rst.txt	46206	0644	edit dl rm
unittest.mock.rst.txt	85991	0644	edit dl rm
unittest.rst.txt	93304	0644	edit dl rm
unix.rst.txt	446	0644	edit dl rm
urllib.error.rst.txt	2199	0644	edit dl rm
urllib.parse.rst.txt	27332	0644	edit dl rm
urllib.request.rst.txt	59360	0644	edit dl rm
urllib.robotparser.rst.txt	2969	0644	edit dl rm
urllib.rst.txt	466	0644	edit dl rm
uu.rst.txt	2387	0644	edit dl rm
uuid.rst.txt	8760	0644	edit dl rm
venv.rst.txt	20621	0644	edit dl rm
warnings.rst.txt	20152	0644	edit dl rm
wave.rst.txt	6870	0644	edit dl rm
weakref.rst.txt	21328	0644	edit dl rm
webbrowser.rst.txt	9783	0644	edit dl rm
windows.rst.txt	272	0644	edit dl rm
winreg.rst.txt	24073	0644	edit dl rm
winsound.rst.txt	5134	0644	edit dl rm
wsgiref.rst.txt	33047	0644	edit dl rm
xdrlib.rst.txt	8078	0644	edit dl rm
xml.dom.minidom.rst.txt	10198	0644	edit dl rm
xml.dom.pulldom.rst.txt	5186	0644	edit dl rm
xml.dom.rst.txt	39507	0644	edit dl rm
xml.etree.elementtree.rst.txt	43871	0644	edit dl rm
xml.rst.txt	6071	0644	edit dl rm
xml.sax.handler.rst.txt	15399	0644	edit dl rm
xml.sax.reader.rst.txt	12133	0644	edit dl rm
xml.sax.rst.txt	7159	0644	edit dl rm
xml.sax.utils.rst.txt	3901	0644	edit dl rm
xmlrpc.client.rst.txt	23071	0644	edit dl rm
xmlrpc.rst.txt	475	0644	edit dl rm
xmlrpc.server.rst.txt	14990	0644	edit dl rm
zipapp.rst.txt	17392	0644	edit dl rm
zipfile.rst.txt	24005	0644	edit dl rm
zipimport.rst.txt	5805	0644	edit dl rm
zlib.rst.txt	13912	0644	edit dl rm
_dummy_thread.rst.txt	762	0644	edit dl rm
_thread.rst.txt	6886	0644	edit dl rm
__future__.rst.txt	5245	0644	edit dl rm
__main__.rst.txt	904	0644	edit dl rm

Edit: /usr/share/doc/python3-docs/html/_sources/library/warnings.rst.txt (20152B)

:mod:`warnings` --- Warning control
===================================

.. module:: warnings
   :synopsis: Issue warning messages and control their disposition.

**Source code:** :source:`Lib/warnings.py`

.. index:: single: warnings

--------------

Warning messages are typically issued in situations where it is useful to alert
the user of some condition in a program, where that condition (normally) doesn't
warrant raising an exception and terminating the program.  For example, one
might want to issue a warning when a program uses an obsolete module.

Python programmers issue warnings by calling the :func:`warn` function defined
in this module.  (C programmers use :c:func:`PyErr_WarnEx`; see
:ref:`exceptionhandling` for details).

Warning messages are normally written to ``sys.stderr``, but their disposition
can be changed flexibly, from ignoring all warnings to turning them into
exceptions.  The disposition of warnings can vary based on the warning category
(see below), the text of the warning message, and the source location where it
is issued.  Repetitions of a particular warning for the same source location are
typically suppressed.

There are two stages in warning control: first, each time a warning is issued, a
determination is made whether a message should be issued or not; next, if a
message is to be issued, it is formatted and printed using a user-settable hook.

The determination whether to issue a warning message is controlled by the
warning filter, which is a sequence of matching rules and actions. Rules can be
added to the filter by calling :func:`filterwarnings` and reset to its default
state by calling :func:`resetwarnings`.

The printing of warning messages is done by calling :func:`showwarning`, which
may be overridden; the default implementation of this function formats the
message by calling :func:`formatwarning`, which is also available for use by
custom implementations.

.. seealso::
   :func:`logging.captureWarnings` allows you to handle all warnings with
   the standard logging infrastructure.

.. _warning-categories:

Warning Categories
------------------

There are a number of built-in exceptions that represent warning categories.
This categorization is useful to be able to filter out groups of warnings.  The
following warnings category classes are currently defined:

.. tabularcolumns:: |l|p{0.6\linewidth}|

+----------------------------------+-----------------------------------------------+
| Class                            | Description                                   |
+==================================+===============================================+
| :exc:`Warning`                   | This is the base class of all warning         |
|                                  | category classes.  It is a subclass of        |
|                                  | :exc:`Exception`.                             |
+----------------------------------+-----------------------------------------------+
| :exc:`UserWarning`               | The default category for :func:`warn`.        |
+----------------------------------+-----------------------------------------------+
| :exc:`DeprecationWarning`        | Base category for warnings about deprecated   |
|                                  | features (ignored by default).                |
+----------------------------------+-----------------------------------------------+
| :exc:`SyntaxWarning`             | Base category for warnings about dubious      |
|                                  | syntactic features.                           |
+----------------------------------+-----------------------------------------------+
| :exc:`RuntimeWarning`            | Base category for warnings about dubious      |
|                                  | runtime features.                             |
+----------------------------------+-----------------------------------------------+
| :exc:`FutureWarning`             | Base category for warnings about constructs   |
|                                  | that will change semantically in the future.  |
+----------------------------------+-----------------------------------------------+
| :exc:`PendingDeprecationWarning` | Base category for warnings about features     |
|                                  | that will be deprecated in the future         |
|                                  | (ignored by default).                         |
+----------------------------------+-----------------------------------------------+
| :exc:`ImportWarning`             | Base category for warnings triggered during   |
|                                  | the process of importing a module (ignored by |
|                                  | default).                                     |
+----------------------------------+-----------------------------------------------+
| :exc:`UnicodeWarning`            | Base category for warnings related to         |
|                                  | Unicode.                                      |
+----------------------------------+-----------------------------------------------+
| :exc:`BytesWarning`              | Base category for warnings related to         |
|                                  | :class:`bytes` and :class:`bytearray`.        |
+----------------------------------+-----------------------------------------------+
| :exc:`ResourceWarning`           | Base category for warnings related to         |
|                                  | resource usage.                               |
+----------------------------------+-----------------------------------------------+

While these are technically built-in exceptions, they are documented here,
because conceptually they belong to the warnings mechanism.

User code can define additional warning categories by subclassing one of the
standard warning categories.  A warning category must always be a subclass of
the :exc:`Warning` class.

.. _warning-filter:

The Warnings Filter
-------------------

The warnings filter controls whether warnings are ignored, displayed, or turned
into errors (raising an exception).

Conceptually, the warnings filter maintains an ordered list of filter
specifications; any specific warning is matched against each filter
specification in the list in turn until a match is found; the match determines
the disposition of the match.  Each entry is a tuple of the form (*action*,
*message*, *category*, *module*, *lineno*), where:

* *action* is one of the following strings:

* *message* is a string containing a regular expression that the start of
  the warning message must match.  The expression is compiled to always be
  case-insensitive.

* *category* is a class (a subclass of :exc:`Warning`) of which the warning
  category must be a subclass in order to match.

* *module* is a string containing a regular expression that the module name must
  match.  The expression is compiled to be case-sensitive.

* *lineno* is an integer that the line number where the warning occurred must
  match, or ``0`` to match all line numbers.

Since the :exc:`Warning` class is derived from the built-in :exc:`Exception`
class, to turn a warning into an error we simply raise ``category(message)``.

The warnings filter is initialized by :option:`-W` options passed to the Python
interpreter command line.  The interpreter saves the arguments for all
:option:`-W` options without interpretation in ``sys.warnoptions``; the
:mod:`warnings` module parses these when it is first imported (invalid options
are ignored, after printing a message to ``sys.stderr``).

Default Warning Filters
~~~~~~~~~~~~~~~~~~~~~~~

By default, Python installs several warning filters, which can be overridden by
the command-line options passed to :option:`-W` and calls to
:func:`filterwarnings`.

* :exc:`DeprecationWarning` and :exc:`PendingDeprecationWarning`, and
  :exc:`ImportWarning` are ignored.

* :exc:`BytesWarning` is ignored unless the :option:`-b` option is given once or
  twice; in this case this warning is either printed (``-b``) or turned into an
  exception (``-bb``).

* :exc:`ResourceWarning` is ignored unless Python was built in debug mode.

.. versionchanged:: 3.2
   :exc:`DeprecationWarning` is now ignored by default in addition to
   :exc:`PendingDeprecationWarning`.

.. _warning-suppress:

Temporarily Suppressing Warnings
--------------------------------

If you are using code that you know will raise a warning, such as a deprecated
function, but do not want to see the warning, then it is possible to suppress
the warning using the :class:`catch_warnings` context manager::

import warnings

def fxn():
        warnings.warn("deprecated", DeprecationWarning)

with warnings.catch_warnings():
        warnings.simplefilter("ignore")
        fxn()

While within the context manager all warnings will simply be ignored. This
allows you to use known-deprecated code without having to see the warning while
not suppressing the warning for other code that might not be aware of its use
of deprecated code.  Note: this can only be guaranteed in a single-threaded
application. If two or more threads use the :class:`catch_warnings` context
manager at the same time, the behavior is undefined.

.. _warning-testing:

Testing Warnings
----------------

To test warnings raised by code, use the :class:`catch_warnings` context
manager. With it you can temporarily mutate the warnings filter to facilitate
your testing. For instance, do the following to capture all raised warnings to
check::

import warnings

def fxn():
        warnings.warn("deprecated", DeprecationWarning)

with warnings.catch_warnings(record=True) as w:
        # Cause all warnings to always be triggered.
        warnings.simplefilter("always")
        # Trigger a warning.
        fxn()
        # Verify some things
        assert len(w) == 1
        assert issubclass(w[-1].category, DeprecationWarning)
        assert "deprecated" in str(w[-1].message)

One can also cause all warnings to be exceptions by using ``error`` instead of
``always``. One thing to be aware of is that if a warning has already been
raised because of a ``once``/``default`` rule, then no matter what filters are
set the warning will not be seen again unless the warnings registry related to
the warning has been cleared.

Once the context manager exits, the warnings filter is restored to its state
when the context was entered. This prevents tests from changing the warnings
filter in unexpected ways between tests and leading to indeterminate test
results. The :func:`showwarning` function in the module is also restored to
its original value.  Note: this can only be guaranteed in a single-threaded
application. If two or more threads use the :class:`catch_warnings` context
manager at the same time, the behavior is undefined.

When testing multiple operations that raise the same kind of warning, it
is important to test them in a manner that confirms each operation is raising
a new warning (e.g. set warnings to be raised as exceptions and check the
operations raise exceptions, check that the length of the warning list
continues to increase after each operation, or else delete the previous
entries from the warnings list before each new operation).

.. _warning-ignored:

Updating Code For New Versions of Python
----------------------------------------

Warnings that are only of interest to the developer are ignored by default. As
such you should make sure to test your code with typically ignored warnings
made visible. You can do this from the command-line by passing :option:`-Wd <-W>`
to the interpreter (this is shorthand for :option:`!-W default`).  This enables
default handling for all warnings, including those that are ignored by default.
To change what action is taken for encountered warnings you simply change what
argument is passed to :option:`-W`, e.g. :option:`!-W error`. See the
:option:`-W` flag for more details on what is possible.

To programmatically do the same as :option:`!-Wd`, use::

warnings.simplefilter('default')

Make sure to execute this code as soon as possible. This prevents the
registering of what warnings have been raised from unexpectedly influencing how
future warnings are treated.

Having certain warnings ignored by default is done to prevent a user from
seeing warnings that are only of interest to the developer. As you do not
necessarily have control over what interpreter a user uses to run their code,
it is possible that a new version of Python will be released between your
release cycles.  The new interpreter release could trigger new warnings in your
code that were not there in an older interpreter, e.g.
:exc:`DeprecationWarning` for a module that you are using. While you as a
developer want to be notified that your code is using a deprecated module, to a
user this information is essentially noise and provides no benefit to them.

The :mod:`unittest` module has been also updated to use the ``'default'``
filter while running tests.

.. _warning-functions:

Available Functions
-------------------

.. function:: warn(message, category=None, stacklevel=1, source=None)

Issue a warning, or maybe ignore it or raise an exception.  The *category*
   argument, if given, must be a warning category class (see above); it defaults to
   :exc:`UserWarning`.  Alternatively *message* can be a :exc:`Warning` instance,
   in which case *category* will be ignored and ``message.__class__`` will be used.
   In this case the message text will be ``str(message)``. This function raises an
   exception if the particular warning issued is changed into an error by the
   warnings filter see above.  The *stacklevel* argument can be used by wrapper
   functions written in Python, like this::

def deprecation(message):
          warnings.warn(message, DeprecationWarning, stacklevel=2)

This makes the warning refer to :func:`deprecation`'s caller, rather than to the
   source of :func:`deprecation` itself (since the latter would defeat the purpose
   of the warning message).

*source*, if supplied, is the destroyed object which emitted a
   :exc:`ResourceWarning`.

.. versionchanged:: 3.6
      Added *source* parameter.

.. function:: warn_explicit(message, category, filename, lineno, module=None, registry=None, module_globals=None, source=None)

This is a low-level interface to the functionality of :func:`warn`, passing in
   explicitly the message, category, filename and line number, and optionally the
   module name and the registry (which should be the ``__warningregistry__``
   dictionary of the module).  The module name defaults to the filename with
   ``.py`` stripped; if no registry is passed, the warning is never suppressed.
   *message* must be a string and *category* a subclass of :exc:`Warning` or
   *message* may be a :exc:`Warning` instance, in which case *category* will be
   ignored.

*module_globals*, if supplied, should be the global namespace in use by the code
   for which the warning is issued.  (This argument is used to support displaying
   source for modules found in zipfiles or other non-filesystem import
   sources).

*source*, if supplied, is the destroyed object which emitted a
   :exc:`ResourceWarning`.

.. versionchanged:: 3.6
      Add the *source* parameter.

.. function:: showwarning(message, category, filename, lineno, file=None, line=None)

Write a warning to a file.  The default implementation calls
   ``formatwarning(message, category, filename, lineno, line)`` and writes the
   resulting string to *file*, which defaults to ``sys.stderr``.  You may replace
   this function with any callable by assigning to ``warnings.showwarning``.
   *line* is a line of source code to be included in the warning
   message; if *line* is not supplied, :func:`showwarning` will
   try to read the line specified by *filename* and *lineno*.

.. function:: formatwarning(message, category, filename, lineno, line=None)

Format a warning the standard way.  This returns a string which may contain
   embedded newlines and ends in a newline.  *line* is a line of source code to
   be included in the warning message; if *line* is not supplied,
   :func:`formatwarning` will try to read the line specified by *filename* and
   *lineno*.

.. function:: filterwarnings(action, message='', category=Warning, module='', lineno=0, append=False)

Insert an entry into the list of :ref:`warnings filter specifications
   <warning-filter>`.  The entry is inserted at the front by default; if
   *append* is true, it is inserted at the end.  This checks the types of the
   arguments, compiles the *message* and *module* regular expressions, and
   inserts them as a tuple in the list of warnings filters.  Entries closer to
   the front of the list override entries later in the list, if both match a
   particular warning.  Omitted arguments default to a value that matches
   everything.

.. function:: simplefilter(action, category=Warning, lineno=0, append=False)

Insert a simple entry into the list of :ref:`warnings filter specifications
   <warning-filter>`.  The meaning of the function parameters is as for
   :func:`filterwarnings`, but regular expressions are not needed as the filter
   inserted always matches any message in any module as long as the category and
   line number match.

.. function:: resetwarnings()

Reset the warnings filter.  This discards the effect of all previous calls to
   :func:`filterwarnings`, including that of the :option:`-W` command line options
   and calls to :func:`simplefilter`.

Available Context Managers
--------------------------

.. class:: catch_warnings(\*, record=False, module=None)

A context manager that copies and, upon exit, restores the warnings filter
    and the :func:`showwarning` function.
    If the *record* argument is :const:`False` (the default) the context manager
    returns :class:`None` on entry. If *record* is :const:`True`, a list is
    returned that is progressively populated with objects as seen by a custom
    :func:`showwarning` function (which also suppresses output to ``sys.stdout``).
    Each object in the list has attributes with the same names as the arguments to
    :func:`showwarning`.

The *module* argument takes a module that will be used instead of the
    module returned when you import :mod:`warnings` whose filter will be
    protected. This argument exists primarily for testing the :mod:`warnings`
    module itself.

.. note::

The :class:`catch_warnings` manager works by replacing and
        then later restoring the module's
        :func:`showwarning` function and internal list of filter
        specifications.  This means the context manager is modifying
        global state and therefore is not thread-safe.

cmd: