Option to make the lru_cache type specific

[rhettinger]

BPO	13227
Nosy	@rhettinger, @ncoghlan, @vstinner, @ezio-melotti
Files	typed_lru.diff: Add type differentiation to the cache entries typed_lru2.diff: Patch with tests and application to re module typed_lru3.diff: Updated patch with docs

^{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 = 'https://github.com/rhettinger'
closed_at = <Date 2011-10-20.15:59:28.817>
created_at = <Date 2011-10-19.22:06:36.315>
labels = ['type-feature', 'library']
title = 'Option to make the lru_cache type specific'
updated_at = <Date 2011-10-20.15:59:28.815>
user = 'https://github.com/rhettinger'

bugs.python.org fields:

activity = <Date 2011-10-20.15:59:28.815>
actor = 'rhettinger'
assignee = 'rhettinger'
closed = True
closed_date = <Date 2011-10-20.15:59:28.817>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2011-10-19.22:06:36.315>
creator = 'rhettinger'
dependencies = []
files = ['23473', '23475', '23480']
hgrepos = []
issue_num = 13227
keywords = ['patch']
message_count = 8.0
messages = ['145976', '145985', '145990', '145994', '146007', '146008', '146022', '146023']
nosy_count = 5.0
nosy_names = ['rhettinger', 'ncoghlan', 'vstinner', 'ezio.melotti', 'python-dev']
pr_nums = []
priority = 'low'
resolution = 'fixed'
stage = 'patch review'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue13227'
versions = ['Python 3.3']

[rhettinger]

Based on a comment from Andrew Koenig, it is suggested that the lru_cache() offer an option to become type specific so that equal objects of different typed don't get cached to the same entry.

Here's an example:

@lru_cache(typed=True)
def square(x):
    print('squaring', x)
    return x * x

for x in [3, 3.0, 3, 3.0]:
    print(square(x))

Without type specificity, all four calls will return 9 rather than 9. 9.0, 9, 9.0.

First-pass patch attached.

[rhettinger]

Updated patch to include tests and an application to the re module.

[vstinner]

The patch doesn't update the doc. You may also test type(square(3)). Except of these nits, the patch looks good.

The typed option is an important feature, and your patch contains a good example of its usage (the re module).

[ncoghlan]

Features looks good, but the current patch doesn't handle keyword arguments correctly (more details in the Reitveld review).

[rhettinger]

Nick, Ezio, and Victor, thanks for looking at the code.
Here's an updated the patch:

• optimization for fast globals() are now keyword-only arguments
• now types the keyword values, not the key/values tuples
• expanded tests
• added the doc update

[ncoghlan]

Looks good to me (although it took me longer than it should have to figure out why you didn't need to store the keyword argument names a second time)

[python-dev]

New changeset cba503a2c468 by Raymond Hettinger in branch 'default':
bpo-13227: Option to make the lru_cache() type specific (suggested by Andrew Koenig).
http://hg.python.org/cpython/rev/cba503a2c468

[rhettinger]

Victor, Ezio, and Nick, thanks for the review.
Andrew, thanks for the feature request.