bleach unconstrained dependency causes import errors

[ReubenFrankel]

The bleach package was updated to version 5.0.0 earlier today. This broke importing modules from nbconvert on the latest version (6.4.5). This seems to be an issue with older 6.4 versions as well.

The bleach dependency is currently unconstrained:

nbconvert/setup.py

Line 248 in 68b496b

"bleach",

We tested with the previous major version of bleach (4.1.0), which resolved the issue.

---

Steps to reproduce

(tested with Python 3.7.13 and 3.9.5)

pip install nbconvert

from nbconvert import MarkdownExporter

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/__init__.py", line 4, in <module>
    from .exporters import *
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/exporters/__init__.py", line 3, in <module>
    from .html import HTMLExporter
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/exporters/html.py", line 26, in <module>
    from nbconvert.filters.highlight import Highlight2HTML
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/filters/__init__.py", line 6, in <module>
    from .markdown import *
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/filters/markdown.py", line 23, in <module>
    from .pandoc import convert_pandoc
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/filters/pandoc.py", line 1, in <module>
    from nbconvert.utils.pandoc import pandoc
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/utils/pandoc.py", line 12, in <module>
    from nbconvert.utils.version import check_version
  File "/private/tmp/.venv/lib/python3.7/site-packages/nbconvert/utils/version.py", line 11, in <module>
    from packaging.version import Version
ModuleNotFoundError: No module named 'packaging'

[bollwyvl]

ideally, we'd be able to add a dependency on packaging, which #1755 is exploring. it's already a dependency of many downstreams.

[bollwyvl]

update: #1755 offers one approach to move forward. we'll see if others want to do alternative PRs.

[blink1073]

Fixed by #1755