Add option to prevent default type translations

[seanpk]

🚀 Feature

Add an option to runPython (and related functions) to NOT translate values back to JavaScript, but instead provide a PyProxy object.

Motivation

Some Python libraries make types based on enum and expect them as parameters. They do not accept the integer 3 when calling a function, but require that Foo.bar be provide.

Pitch

To solve this, I would like to be able to use runPython for a special case that doesn't do the type translation, e.g.:

const enumValue = pyodide.runPython(`
    import foo
    Foo.bar
  `, { skipTranslation: true })
pyproxyObjectThatTookALotOfWorkToCreate.magicFunction(enumValue)

Alternatives

Without this feature, I don't see how to call the function without moving (nearly) the whole algorithm into a runPython call.

[hoodmane]

Does this work?

const enumValue = pyodide.runPython(`
   from pyodide.ffi import create_proxy
   create_proxy(Foo.bar)
`);

[seanpk]

Unfortunately, no; it is still coming out as an integer. :-(

Looking closer at the library I'm calling, they have implemented a enum.IntEnum, which should be convertible to and from an integer value, and so I'm pretty sure the default behavior of pyodide would be OK. However, in the function I'm calling they're doing an isinstance test so I still need the actual enum object to make it work.

That said, I have found a workaround I think is OK:

const locals = {
  the_magic_object: pyproxyObjectThatTookALotOfWorkToCreate,
  the_enum_int_value: functionThatFiguresOutTheRightValue(),
  ...allTheOtherVarialblesNeededToCallTheFunction
}
const script = `
  from bar import foo
  foo_enum = Foo(the_enum_int_value)
  the_magic_object.magic_function(foo_enum, ...)
`
pyodide.runPython(script, { locals })

It still may be worthwhile being able to disable translations at times, but I'm not blocked until that is decided and figured out.

Thanks!

[hoodmane]

Seems to work for me.

const v = pyodide.runPython(`
   from pyodide.ffi import create_proxy
   from enum import Enum
   class A(Enum):
      v = 1

create_proxy(A.v, roundtrip=False)
`);
const  f = pyodide.runPython(`
   def f(x):
      print("x is A.v?", x is A.v)
   f
`);

f(v)

Prints x is A.v? True

[seanpk]

I'll have to try again with the roundtrip=False option.