Upgrade to SymPy 1.3

[slelievre]

Sympy 1.3 was released on 2018-09-14.

• Tarball: ​https://files.pythonhosted.org/packages/dd/f6/ed485ff22efdd7b371d0dbbf6d77ad61c3b3b7e0815a83c89cbb38ce35de/sympy-1.3.tar.gz

Our last upgrade was to Sympy 1.2 in #26117.

[fbissey]

Sadly this release still doesn't include sage's patch defining and using UndefSage. I am guessing it is still necessary.

[fbissey]

Replying to fbissey:

Sadly this release still doesn't include sage's patch defining and using UndefSage. I am guessing it is still necessary.

And that's the only thing failing if you stick to plain unpatched sympy-1.3

sage -t --long /usr/lib64/python2.7/site-packages/sage/interfaces/sympy.py
**********************************************************************
File "/usr/lib64/python2.7/site-packages/sage/interfaces/sympy.py", line 859, in sage.interfaces.sympy.test_all
Failed example:
    test_all()
Exception raised:
    Traceback (most recent call last):
      File "/usr/lib64/python2.7/site-packages/sage/doctest/forker.py", line 671, in _run
        self.compile_and_execute(example, compiler, test.globs)
      File "/usr/lib64/python2.7/site-packages/sage/doctest/forker.py", line 1086, in compile_and_execute
        exec(compiled, globs)
      File "<doctest sage.interfaces.sympy.test_all[1]>", line 1, in <module>
        test_all()
      File "/usr/lib64/python2.7/site-packages/sage/interfaces/sympy.py", line 969, in test_all
        test_undefined_function()
      File "/usr/lib64/python2.7/site-packages/sage/interfaces/sympy.py", line 958, in test_undefined_function
        assert f == sf._sage_()
    TypeError: unbound method _sympysage_function() must be called with f instance as first argument (got nothing instead)
**********************************************************************

which is of course what the patch fixes.

[fbissey]

Ready for review.

---

New commits:

​8c64ecf

update sympy to 1.3

[fbissey]

Ping?