Allow profile/cProfile to be used as context managers

[ThaneBrimhall]

BPO	29235
Nosy	@brettcannon, @methane, @ethanfurman, @serhiy-storchaka, @zhangyangyu, @ssanderson, @csabella
PRs	bpo-29235: Make cProfile.Profile a context manager. #6808 bpo-29235: Update document for Profiler's context manager #7331
Files	profileContextManager.patch

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2019-01-29.13:26:26.543>
created_at = <Date 2017-01-11.01:13:40.405>
labels = ['3.8', 'type-feature', 'library']
title = 'Allow profile/cProfile to be used as context managers'
updated_at = <Date 2019-01-29.13:26:26.538>
user = 'https://bugs.python.org/ThaneBrimhall'

bugs.python.org fields:

activity = <Date 2019-01-29.13:26:26.538>
actor = 'cheryl.sabella'
assignee = 'none'
closed = True
closed_date = <Date 2019-01-29.13:26:26.543>
closer = 'cheryl.sabella'
components = ['Library (Lib)']
creation = <Date 2017-01-11.01:13:40.405>
creator = 'Thane Brimhall'
dependencies = []
files = ['46295']
hgrepos = []
issue_num = 29235
keywords = ['patch']
message_count = 10.0
messages = ['285175', '285535', '285536', '285538', '316533', '318459', '318460', '318471', '318917', '334514']
nosy_count = 9.0
nosy_names = ['brett.cannon', 'methane', 'ethan.furman', 'serhiy.storchaka', 'xiang.zhang', 'Scott Sanderson', 'Thane Brimhall', 'cheryl.sabella', 'Scott Sanderson2']
pr_nums = ['6808', '7331']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue29235'
versions = ['Python 3.8']

[ThaneBrimhall]

The enable and disable methods on the profilers fit the description of a context manager very well. The following code:

    pr = cProfile.Profile()
    pr.enable()
    # ... do something ...
    pr.disable()
    pr.print_stats()

Would turn into something like this:

    with cProfile.Profile() as pr:
        # ... do something ...
    pr.print_stats()

The patch for this code would be trivial and backwards-compatible: simply add something like the following lines to the _lsprof.Profiler base class:

    def __enter__(self):
        self.enable()
        return self

    def __exit__(self, exc_type, exc_val, exc_tb):
        self.disable()

[ThaneBrimhall]

So this is my first time contributing to Python, but here's a (trivial) patch for this issue. Let me know what else is required to make this happen. I suspect unit tests and documentation updates?

[zhangyangyu]

I suspect unit tests and documentation updates?

Yes. Code alone is not enough. It's better to have tests and documentation. Also, it's appreciated to sign the CLA: https://www.python.org/psf/contrib/contrib-form/. :-)

[ThaneBrimhall]

I've signed the agreement. I will do the necessary research to figure out how to do unit tests and documentation updates.

I should also mention that while maintaining API-compatibility with profile was a stated goal, it turns out that the pure-python profiler actually does not have the enable() and disable() methods that the context manager needs.

[ssanderson]

This looks like it's been dormant for a bit. I've posted a patch (with tests and docs) to #6808.

[brettcannon]

New changeset 2e01b75 by Brett Cannon (Scott Sanderson) in branch 'master':
bpo-29235: Make cProfile.Profile a context manager (GH-6808)
2e01b75

[serhiy-storchaka]

Please add a versionadded or versionchanged directive in the documentation (not sure what is more appropriate in this case) and an entry in What's New.

A news entry shouldn't consist of several paragraphs. This will be lost when news entries will be merged into a single NEWS file.

[ScottSanderson2]

I've posted a patch to update the docs to #7331.

[methane]

New changeset cebe80b by INADA Naoki (Scott Sanderson) in branch 'master':
bpo-29235: Update document for Profiler's context manager (GH-7331)
cebe80b

[csabella]

Closing as these changes have been merged for a few months.

msg285538 mentions that the pure-Python profiler doesn't have enable and disable, which is already opened in bpo-32017.