Faster ElementTree deepcopying

[serhiy-storchaka]

BPO	25869
Nosy	@brettcannon, @scoder, @serhiy-storchaka
Files	bench_etree_deepcopy.log: Benchmark results etree_deepcopy.patch etree_deepcopy2.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 = 'https://github.com/serhiy-storchaka'
closed_at = <Date 2015-12-21.11:50:59.673>
created_at = <Date 2015-12-15.10:48:06.969>
labels = ['extension-modules', 'performance']
title = 'Faster ElementTree deepcopying'
updated_at = <Date 2015-12-21.11:50:59.672>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2015-12-21.11:50:59.672>
actor = 'serhiy.storchaka'
assignee = 'serhiy.storchaka'
closed = True
closed_date = <Date 2015-12-21.11:50:59.673>
closer = 'serhiy.storchaka'
components = ['Extension Modules']
creation = <Date 2015-12-15.10:48:06.969>
creator = 'serhiy.storchaka'
dependencies = []
files = ['41315', '41316', '41317']
hgrepos = []
issue_num = 25869
keywords = ['patch']
message_count = 3.0
messages = ['256455', '256459', '256796']
nosy_count = 4.0
nosy_names = ['brett.cannon', 'scoder', 'python-dev', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'performance'
url = 'https://bugs.python.org/issue25869'
versions = ['Python 3.6']

[serhiy-storchaka]

According to lxml benchmark [1], deepcopying a tree in ElementTree is about 20 times slower than in lxml. Proposed patch optimizes deepcopying C implementation of ElementTree about 20 times. It is now 5% to 3 times faster than in lxml.

[1] http://lxml.de/performance.html

[serhiy-storchaka]

Updated patch correctly handles rare cases when different elements share the same attrib dict and when the same Element is occurred on different places in ElementTree (that is no longer a tree, but a directed graph).

[python-dev]

New changeset 090c3e3a648d by Serhiy Storchaka in branch 'default':
Issue bpo-25869: Optimized deepcopying ElementTree; it is now 20 times faster.
https://hg.python.org/cpython/rev/090c3e3a648d