[WIP] Make SymPy depend on 3rd party multipledispatch module

[oscarbenjamin]

References to other Issues or PRs

An alternative to #23621. This does not yet fix the import time problem though.

Brief description of what is fixed or changed

Change all usage of sympy.multipledispatch to import from and use multipledispatch. Add a dependency on the 3rd party Python multipledispatch module.

There are some incompatibilities between SymPy's multipledispatch and the PyPI package that need to be resolved before fully deleting the module:

• [X] Change all imports
• [X] Add dependency in setup.py
• [X] Install in CI
• [ ] Make sure all tests pass
• [ ] Resolve any incompatibilities
• [ ] Move any code in the sympy.multipledispatch module somewhere else (maybe there could be sympy/external/multipledispatch).
• [ ] Delete the sympy.multipledispatch module and associated tests
• [ ] Remove all references e.g. in setup.py, LICENSE, etc
• [ ] Improve import time
• [ ] Update docs

Other comments

The 3rd party multipledispatch module does not seem to be actively maintained e.g. it hasn't had a release since 4 years ago in 2018. It's not clear that it really needs much in terms of fixes though because it is relatively simple.

We might not want to depend on it as a 3rd party package but if not then at least we should update the vendored version to match the latest PyPI release because it has a number of improvements. At least there has been one fix in SymPy (#22029) that has not been applied to the 3rd party package https://github.com/mrocklin/multipledispatch/issues/118.

Alternatively if it does need more maintenance maybe it would be possible to take over maintenance.

Release Notes

• other
  • SymPy now depends on the third party multipledispatch module (as installed by pip install multipledispatch) rather the vendoring its own older version of the same module.

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• other
  • SymPy now depends on the third party multipledispatch module (as installed by pip install multipledispatch) rather the vendoring its own older version of the same module. (#23830 by @oscarbenjamin)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.12.

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#### References to other Issues or PRs
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An alternative to #23621. This does not yet fix the import time problem though.

#### Brief description of what is fixed or changed

Change all usage of `sympy.multipledispatch` to import from and use `multipledispatch`. Add a dependency on the 3rd party Python `multipledispatch` module.

There are some incompatibilities between SymPy's multipledispatch and the PyPI package that need to be resolved before fully deleting the module:

- [X] Change all imports
- [X] Add dependency in setup.py
- [X] Install in CI
- [ ] Make sure all tests pass
- [ ] Resolve any incompatibilities
- [ ] Move any code in the `sympy.multipledispatch` module somewhere else (maybe there could be `sympy/external/multipledispatch`).
- [ ] Delete the `sympy.multipledispatch` module and associated tests
- [ ] Remove all references e.g. in setup.py, LICENSE, etc
- [ ] Improve import time
- [ ] Update docs

#### Other comments

The 3rd party multipledispatch module does not seem to be actively maintained e.g. it hasn't had a release since 4 years ago in 2018. It's not clear that it really needs much in terms of fixes though because it is relatively simple.

We might not want to depend on it as a 3rd party package but if not then at least we should update the vendored version to match the latest PyPI release because it has a number of improvements. At least there has been one fix in SymPy (#22029) that has not been applied to the 3rd party package https://github.com/mrocklin/multipledispatch/issues/118.

Alternatively if it does need more maintenance maybe it would be possible to take over maintenance.

#### Release Notes

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  * Added a new solver for logarithmic equations.

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  * Fixed a bug with log of integers.

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<!-- BEGIN RELEASE NOTES -->
* other
  * SymPy now depends on the third party multipledispatch module (as installed by `pip install multipledispatch`) rather the vendoring its own older version of the same module.
<!-- END RELEASE NOTES -->

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[asmeurer]

The 3rd party multipledispatch module does not seem to be actively maintained e.g. it hasn't had a release since 4 years ago in 2018. It's not clear that it really needs much in terms of fixes though because it is relatively simple.

We might not want to depend on it as a 3rd party package but if not then at least we should update the vendored version to match the latest PyPI release because it has a number of improvements. At least there has been one fix in SymPy (https://github.com/sympy/sympy/pull/22029) that has not been applied to the 3rd party package https://github.com/mrocklin/multipledispatch/issues/118.

Alternatively if it does need more maintenance maybe it would be possible to take over maintenance.

That's my only concern here. However, if there is interest in taking over maintenance, perhaps @mrocklin would be open to the idea.

[mrocklin]

I'd be happy to expand ownership of that repository to a trusted individual. I'd trust @asmeurer if he's volunteering :slightly_smiling_face:

[asmeurer]

I think @oscarbenjamin is actually the one who's volunteering, but if your trust only extends as far as me I can take that on for now.

[oscarbenjamin]

I would rather it be an organisational basis like "sympy" would take over maintenance if that is needed. I think that it is generally better to think of maintenance in terms of organisations rather than individuals if possible.

[sylee957]

The future in python 3.10 allows structual pattern matching which can outdate some functional capability of multipledispatch.