| msg316416 - (view) |
Author: Alyssa Coghlan (ncoghlan) *  |
Date: 2018-05-11 22:31 |
| The current example for contextlib.contextmanager doesn't use try/finally, which sets folks up for writing resource management context managers that don't clean up after exceptions properly. There's an example with try/finally down in the contextlib.closing docs, but I'm thinking it would be worthwhile to change the presentation of contextmanager itself. |
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| msg320035 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2018-06-20 08:19 |
| It doesn't look as a good example. It is not always good to write a closing tag if an error was occurred while write an inner content. In many cases it is better to stop writing after error. |
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| msg320069 - (view) |
Author: Alyssa Coghlan (ncoghlan) * |
Date: 2018-06-20 11:23 |
| Right, the HTML example was always a bit cutesy (hence the disclaimer in the header), but it's hard to come up with a good illustrative example that isn't already a native context manager in the standard library. Perhaps it would make sense to change the example text completely, and write something entirely abstract like: from contextlib import contextmanager @contextmanager def managed_resource(*args, **kwds): # Code to acquire resource, e.g.: resource = acquire_resource(*args, **kwds) try: yield resource finally: # Code to release resource, e.g.: release_resource(resource) >>> with managed_resource(*args, **kwds) as resource: ... # Resource is released at the end of this block, ... # even if code in the block raises an exception Then the introductory text could be updated to say something like "While many objects natively support use in with statements, sometimes a resource needs to be managed that isn't a context manager in its own right, and doesn't implement a ``close()`` method for use with ``contextlib.closing``.". |
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| msg320365 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-06-24 08:13 |
| A possible concrete example: Capturing sys.stdout and/or sys.stderr for testing, as in test.support.captured_output. |
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| msg320367 - (view) |
Author: Alyssa Coghlan (ncoghlan) * |
Date: 2018-06-24 09:05 |
| Similar to closing, we have dedicated context managers for stdout and stderr redirection now: https://docs.python.org/3/library/contextlib.html#contextlib.redirect_stdout Redirecting stdin could be a good example though, since we've so far chosen not to provide a standard context manager for that (it's a sufficiently uncommon use case that we haven't seen the need to add it directly). |
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| msg320369 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2018-06-24 12:05 |
| The entirely abstract example LGTM. As for concrete real word examples, the possible one is changing the current working directory: cwd = os.getcwd() try: os.chdir(target_dir) yield finally: os.chdir(cwd) |
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| msg320781 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-06-30 13:38 |
| Nick's abstract example LGTM as well. |
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| msg322258 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-07-23 21:10 |
| New changeset bde782bb594edffeabe978abeee2b7082ab9bc2a by Tal Einat (Matthias Bussonnier) in branch 'master': bpo-33468: Add try-finally contextlib.contextmanager example (GH-7816) https://github.com/python/cpython/commit/bde782bb594edffeabe978abeee2b7082ab9bc2a |
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| msg322261 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-07-23 21:38 |
| New changeset 4e166ffd29b675238ccd94964743f6cb206d2235 by Tal Einat (Miss Islington (bot)) in branch '3.7': bpo-33468: Add try-finally contextlib.contextmanager example (GH-7816) (GH-8425) https://github.com/python/cpython/commit/4e166ffd29b675238ccd94964743f6cb206d2235 |
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| msg322262 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-07-23 21:38 |
| New changeset 5b3643d1a5114551350a9d17fb0aaab2d503c290 by Tal Einat (Miss Islington (bot)) in branch '3.6': bpo-33468: Add try-finally contextlib.contextmanager example (GH-7816) (GH-8426) https://github.com/python/cpython/commit/5b3643d1a5114551350a9d17fb0aaab2d503c290 |
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| msg322263 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-07-23 21:38 |
| New changeset f7e60a69485097dc28f000c55615038278f84333 by Tal Einat in branch '2.7': [2.7] bpo-33468: Add try-finally contextlib.contextmanager example (GH-7816) (GH-8427) https://github.com/python/cpython/commit/f7e60a69485097dc28f000c55615038278f84333 |
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| msg322264 - (view) |
Author: Tal Einat (taleinat) * |
Date: 2018-07-23 21:41 |
| Thanks for the PR, Matthias Bussonnier! |
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