Numba function signature that allow different types

Question

I have a class with an attribute sources that can or cannot be defined. Before using numba, I set the variable sources to None when it was undefined, otherwise it was a numpy array.

Now, it seems that this behavior is not allowed by numba. Is this correct? I though to use a boolean variable as a workaround, but this messes up with the signature of the function (property) source:

import numba 
from numba.experimental import jitclass
import numpy as np


spec = [
    ("_is_source_none", numba.bool_),
    ("_sources", numba.int32[:, :])
]


@jitclass(spec)
class MyClass:

    def __init__(self, sources: np.array):
        # Numba does not allow to set a var to None so we need an external variable to track it
        self._is_source_none = True if sources is None else False
        self._sources = sources.astype(np.int32) if sources is not None else np.zeros(shape=(50, 50), dtype=np.int32)

    @property
    def sources(self):
        if self._is_source_none:
            return None
        else:
            return self.sources

if __name__ == "__main__":

    MyClass(
        sources=None
    )

Error:

numba.core.errors.TypingError: Failed in nopython mode pipeline (step: nopython mode backend)
Failed in nopython mode pipeline (step: nopython frontend)
Failed in nopython mode pipeline (step: nopython frontend)
Internal error at resolving type of attribute "sources" of "self".
Failed in nopython mode pipeline (step: nopython frontend)
compiler re-entrant to the same function signature
During: typing of get attribute at <input> (25)
Enable logging at debug level for details.
File "<input>", line 25:
<source missing, REPL/exec in use?>
During: typing of get attribute at <string> (3)
During: typing of get attribute at <string> (3)
File "<string>", line 3:
<source missing, REPL/exec in use?>

Is this even possible in Numba?

Answer 1

The error you get has nothing to do with None and typing. It is due to self.sources in the member function sources not being declared nor initialized while self._sources is and should be used instead.

Note Numba actually supports None values using optional types. You can find more information in the Numba documentation.