Try to import Mapping and MutableMapping from collections.abc

[5j9]

Note that collections.abc has been added in Python 3.3.

Fixes #402

[codecov-io]

Codecov Report

Merging #403 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #403      +/-   ##
==========================================
+ Coverage   90.76%   90.77%   +<.01%     
==========================================
  Files          50       50              
  Lines        6950     6956       +6     
  Branches     1328     1328              
==========================================
+ Hits         6308     6314       +6     
  Misses        483      483              
  Partials      159      159

Impacted Files	Coverage Δ
html5lib/_trie/_base.py	61.53% <100%> (+5.01%)	⬆️
html5lib/treebuilders/dom.py	89.41% <100%> (+0.19%)	⬆️

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[gsnedders]

Thanks for fixing this!

[astrojuanlu]

Would be great to have a release shipping this among the other improvements!

[pllim]

Still no release with this patch after a year? 😢

[zsol]

Edit: apologies for the noise, there's already discussion happening about this in #419.

This is now breaking with Python 3.9:

❯ python
Python 3.9.0a2+ (heads/master:b0d4949, Dec 20 2019, 11:38:30)
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import html5lib
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/site-packages/html5lib/__init__.py", line 25, in <module>
    from .html5parser import HTMLParser, parse, parseFragment
  File "/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/site-packages/html5lib/html5parser.py", line 8, in <module>
    from . import _tokenizer
  File "/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/site-packages/html5lib/_tokenizer.py", line 16, in <module>
    from ._trie import Trie
  File "/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/site-packages/html5lib/_trie/__init__.py", line 3, in <module>
    from .py import Trie as PyTrie
  File "/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/site-packages/html5lib/_trie/py.py", line 6, in <module>
    from ._base import Trie as ABCTrie
  File "/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/site-packages/html5lib/_trie/_base.py", line 3, in <module>
    from collections import Mapping
ImportError: cannot import name 'Mapping' from 'collections' (/home/pi/.pyenv/versions/3.9-dev/lib/python3.9/collections/__init__.py)