bidirectional Symbol conversion

[stevengj]

Currently, PyObject(s::Symbol) produces a Python string, and convert(Symbol, o) converts a Python string object back into a Symbol. However, automatic type conversion does not work, i.e. convert(PyAny, PyObject(:Foo)) produces "Foo" not :Foo.

One way to fix this might be to define a new Python string subtype, and instantiate this type from PyObject(s::Symbol). That way, it will be usable as a string in Python but convert(PyAny, ...) will be able to detect that it is "really" a symbol and convert it appropriately.

[MilesCranmer]

Just found this issue. How much work would this be to implement? Happy to help.

This has presented quite a few problems in PyJulia interfaces; e.g., SymbolicRegression.jl had to start accepting strings instead of symbols for the API, and do the conversion internally. Likewise using several Julia packages from Python is not possible without manually writing conversion methods with julia.eval(...).