Sympify eq in diophantine

[oscarbenjamin]

References to other Issues or PRs

Brief description of what is fixed or changed

Don't catch AttributeError in diophantine and sympify the input equation.

Other comments

Release Notes

• solvers
  • The diophantine solver no longer raises for unsympified inputs.

[sympy-bot]

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• solvers
  • The diophantine solver no longer raises for unsympified inputs. (#18201 by @oscarbenjamin)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.6.

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#### References to other Issues or PRs
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#### Brief description of what is fixed or changed

Don't catch `AttributeError` in diophantine and sympify the input equation.

#### Other comments


#### Release Notes

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<!-- BEGIN RELEASE NOTES -->
* solvers
    * The diophantine solver no longer raises for unsympified inputs.
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.

[codecov]

Codecov Report

Merging #18201 into master will increase coverage by 0.014%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##            master   #18201       +/-   ##
============================================
+ Coverage   74.936%   74.95%   +0.014%     
============================================
  Files          642      642               
  Lines       167128   167130        +2     
  Branches     39331    39331               
============================================
+ Hits        125240   125265       +25     
+ Misses       36351    36323       -28     
- Partials      5537     5542        +5