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bpo-39674: Suggest to test with DeprecationWarning by vstinner · Pull Request #18552 · python/cpython

@vstinner

@vstinner 

Add a section in What's New In Python 3.9 to strongly advice to check
for DeprecationWarning in your Python projects.

@vstinner

@brettcannon: Does it sound like what you proposed in the python-dev thread?

hugovk

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Some minor spelling/language suggestions.

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When Python 2.7 was still supported, many functions were kept for backward
compatibility with Python 2.7. With the end of the Python 2.7 support, these

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compatibility with Python 2.7. With the end of the Python 2.7 support, these
compatibility with Python 2.7. With the end of Python 2.7 support, these

When Python 2.7 was still supported, many functions were kept for backward
compatibility with Python 2.7. With the end of the Python 2.7 support, these
backward compatibility layers have been reomved or will be removed shortly.

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backward compatibility layers have been reomved or will be removed shortly.
backward compatibility layers have been removed, or will be removed soon.
When Python 2.7 was still supported, many functions were kept for backward
compatibility with Python 2.7. With the end of the Python 2.7 support, these
backward compatibility layers have been reomved or will be removed shortly.
Most of them emitted :exc:`DeprecationWarning` warning for several years. For

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Most of them emitted :exc:`DeprecationWarning` warning for several years. For
Most of them emitted a :exc:`DeprecationWarning` warning for several years. For
backward compatibility layers have been reomved or will be removed shortly.
Most of them emitted :exc:`DeprecationWarning` warning for several years. For
example, using ``collections.Mapping`` instead of ``collections.abc.Mapping``
emits a :exc:`DeprecationWarning` since Python 3.3 released in 2012.

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emits a :exc:`DeprecationWarning` since Python 3.3 released in 2012.
emits a :exc:`DeprecationWarning` since Python 3.3, released in 2012.
example, using ``collections.Mapping`` instead of ``collections.abc.Mapping``
emits a :exc:`DeprecationWarning` since Python 3.3 released in 2012.

Test your application with :option:`-W` ``default`` command line option to see

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Test your application with :option:`-W` ``default`` command line option to see
Test your application with the :option:`-W` ``default`` command-line option to see
Test your application with :option:`-W` ``default`` command line option to see
:exc:`DeprecationWarning` and :exc:`PendingDeprecationWarning`, or even with
:option:`-W` ``error`` to treat them as errors. :ref:`Warnings Filter
<warning-filter>` can be used to ignore warnings from third party code.

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<warning-filter>` can be used to ignore warnings from third party code.
<warning-filter>` can be used to ignore warnings from third-party code.

@brettcannon

Yep, this is what I was thinking, but you forgot to mention -X dev 😉 .

@vstinner

@vstinner

Yep, this is what I was thinking, but you forgot to mention -X dev wink .

Right. But you wrote that you wasn't convinced that the relationship between DeprecationWarning and -X dev, so I focused on warnings instead ;-)

@brettcannon

I think it's also worth mentioning -X dev; I probably meant to not only mention it as the only way to surface deprecation warnings.

@vstinner

@vstinner

I think it's also worth mentioning -X dev; I probably meant to not only mention it as the only way to surface deprecation warnings.

Ok, done.

hugovk

@vstinner @hugovk 

Co-Authored-By: Hugo van Kemenade <hugovk@users.noreply.github.com>

@vstinner

Thanks @hugovk for your useful reviews!

@hugovk