Fixes #421 - Make all dependencies optional

[bluetech]

Thank you! It will be great to get rid of all of these dependencies.

I wonder if this is compatible with how django-import-export does things?

[claudep]

I think there are two options:

• if django-import-export wants to support all formats as before, it just has to change its dependencies to include the tablib optional ones.
• if django-import-export wants to let the user choose the installed dependencies, it should do something similar to this patch, and then check with the tablib registry to know if some format is available or not.

I'm happy to help if needed.

[codecov[bot]]

Codecov Report

Merging #425 into master will increase coverage by 0.09%. The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #425      +/-   ##
=========================================
+ Coverage   89.41%   89.5%   +0.09%     
=========================================
  Files          24      25       +1     
  Lines        2446    2468      +22     
=========================================
+ Hits         2187    2209      +22     
  Misses        259     259

Impacted Files	Coverage Δ
src/tablib/core.py	82.61% <100%> (-0.17%)	:arrow_down:
src/tablib/formats/__init__.py	97.14% <100%> (+0.65%)	:arrow_up:
tests/test_tablib.py	98.42% <100%> (+0.01%)	:arrow_up:
src/tablib/exceptions.py	100% <100%> (ø)

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[hugovk]

Perhaps a pip install tablib[all] shortcut could install all?

[hugovk]

And I think this would warrant a version bump.

[claudep]

So is it valid/acceptable to add a line like 'all': ['odfpy', 'markuppy', 'pandas', 'pyyaml', 'xlrd', 'xlwt', 'openpyxl>=2.4.0'], in extras_require?

For the version bump, aren't we going to bump the version for the next release anyway?

[hugovk]

So is it valid/acceptable to add a line like 'all': ['odfpy', 'markuppy', 'pandas', 'pyyaml', 'xlrd', 'xlwt', 'openpyxl>=2.4.0'], in extras_require?

Yes, something like that. compare what attrs does:

https://github.com/python-attrs/attrs/blob/179b1c4bf0fedaa0e0281649719d1f1e0bd51e94/setup.py#L39-L55

For the version bump, aren't we going to bump the version for the next release anyway?

Yep :)

[claudep]

Merged in 626a062, thanks for the review!