| msg155442 - (view) |
Author: py.user (py.user) * |
Date: 2012-03-12 05:28 |
| >>> import re >>> p = re.compile(r'abc(?Pdef)') >>> p.sub(r'\g', 'abcdef123abcdef') 'def123def' >>> p.groupindex['n'] = 2 >>> p.sub(r'\g', 'abcdef123abcdef') 'def123def' >>> p.groupindex {'n': 2} >>> |
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| msg155459 - (view) |
Author: Matthew Barnett (mrabarnett) *  |
Date: 2012-03-12 18:16 |
| The re module creates the dict purely for the benefit of the user, and as it's a normal dict, it's mutable. An alternative would to use an immutable dict or dict-like object, but Python doesn't have such a class, and it's probably not worth writing one just for this use-case. |
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| msg155484 - (view) |
Author: py.user (py.user) * |
Date: 2012-03-12 21:37 |
| Matthew Barnett wrote: > The re module creates the dict purely for the benefit of the user this dict affects on regex.sub() >>> import re >>> p = re.compile(r'abc(?Pdef)') >>> p.groupindex {'n': 1} >>> p.groupindex['n'] = 2 >>> p.sub(r'\g', 'abcdef') Traceback (most recent call last): File "/usr/local/lib/python3.2/sre_parse.py", line 811, in expand_template literals[index] = s = g(group) IndexError: no such group During handling of the above exception, another exception occurred: Traceback (most recent call last): File "", line 1, in File "/usr/local/lib/python3.2/re.py", line 286, in filter return sre_parse.expand_template(template, match) File "/usr/local/lib/python3.2/sre_parse.py", line 815, in expand_template raise error("invalid group reference") sre_constants.error: invalid group reference >>> |
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| msg155546 - (view) |
Author: Matthew Barnett (mrabarnett) * |
Date: 2012-03-13 00:52 |
| It appears I was wrong. :-( The simplest solution in that case is for it to return a _copy_ of the dict. |
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| msg155560 - (view) |
Author: Éric Araujo (eric.araujo) *  |
Date: 2012-03-13 02:34 |
| But regex.sub is affected only if you manually muck with the dict, right? If so, then it looks like a case of “it hurts when I do this” (the doctor’s reply: “Don’t do this.”) |
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| msg155570 - (view) |
Author: py.user (py.user) * |
Date: 2012-03-13 05:02 |
| the first message shows how it can work with a broken dict Éric Araujo wrote: > But regex.sub is affected only if you manually muck with the dict, right? I can get code from anywhere |
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| msg155593 - (view) |
Author: Éric Araujo (eric.araujo) * |
Date: 2012-03-13 11:54 |
| > I can get code from anywhere I am afraid I don’t understand. Could you start again and explain what bug you ran into, i.e. what behavior does not match what the docs say? At present this report looks like it is saying “when I put random things in an internal data structures then bad things happen”, and I don‘t think Python promises to not break when people do random editions to internal data structures. |
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| msg155702 - (view) |
Author: py.user (py.user) * |
Date: 2012-03-14 00:56 |
| I take someone's code make tests for its behavior all tests say "the code is working" I continue to write the code make tests for its behavior all tests say "the code is working" I install it somewhere and it crashes now it is depending on the cache, when this exception is raised Éric Araujo wrote: >and I don‘t think Python promises to not break when people do random editions when people do something wrong, python should raise an exception |
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| msg155734 - (view) |
Author: Georg Brandl (georg.brandl) * |
Date: 2012-03-14 07:26 |
| Looks like a case for a read-only dict/dictproxy :) |
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| msg175494 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2012-11-13 10:14 |
| I fully agree with Éric. Just don't do this. |
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| msg175497 - (view) |
Author: Stefan Krah (skrah) * |
Date: 2012-11-13 11:06 |
| I'm not so sure. If dicts or classes are used for configuration or informational purposes, I prefer them to be locked down. An example of the first is the decimal context, where it was possible to write context.emax = 9 instead of context.Emax = 9 without getting an error. This is an easy mistake to make and can be hard to track down in a large program. The mistake here is maybe less likely, but I agree with Georg that it's a case for a read-only dict/dictproxy. |
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| msg175502 - (view) |
Author: Éric Araujo (eric.araujo) * |
Date: 2012-11-13 16:01 |
| I propose using a MappingProxy type in 3.4 and add an example to the docs for stable versions. |
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| msg175505 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2012-11-13 16:48 |
| Copy or proxy may affect performance. We will need to make benchmarks to see how much. |
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| msg230450 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2014-11-01 15:27 |
| Here are two patches which implement two alternative solutions. They are based on regex code. Dict copying patch matches current regex behavior and needs modifying other code to avoid small slowdown. Artificial example: $ ./python -m timeit -s 'import re; n = 100; m = re.match("".join("(?P<g%d>.)" % g for g in range(n)), "x" * n); t = ",".join(r"\g<g%d>" % g for g in range(n))' -- 'm.expand(t)' Without patch: 7.48 msec per loop With re_groupindex_copy.patch but without modifying _expand: 9.61 msec per loop With re_groupindex_copy.patch and with modifying _expand: 7.41 msec per loop While stdlib code can be modified, this patch can cause small slowdown of some third-party code. Dict proxying patch has no performance effect, but it is slightly less compatible. Some code can accept dict but not dict-like object. |
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| msg234878 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-01-28 09:23 |
| Ping. |
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| msg239041 - (view) |
Author: Serhiy Storchaka (serhiy.storchaka) * |
Date: 2015-03-23 15:27 |
| What approach looks better, a copy or a read-only proxy? |
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| msg239094 - (view) |
Author: py.user (py.user) * |
Date: 2015-03-24 07:35 |
| @Serhiy Storchaka > What approach looks better, a copy or a read-only proxy? ISTM, your proxy patch is better, because it expects an exception rather than silence. |
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| msg239526 - (view) |
Author: Roundup Robot (python-dev) |
Date: 2015-03-29 22:02 |
| New changeset 4d5826fa77a1 by Serhiy Storchaka in branch 'default': Issue #14260: The groupindex attribute of regular expression pattern object https://hg.python.org/cpython/rev/4d5826fa77a1 |
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