Why am I getting 'isinstance': Cannot determine Numba type?

Question

I am new with Numba. I am trying to accelerate a pretty complicated solver. However, I keep getting an error such as

numba.core.errors.TypingError: Failed in nopython mode pipeline (step: nopython frontend) Untyped global name 'isinstance': Cannot determine Numba type of <class 'builtin_function_or_method'>

I wrote a small example to reproduce the same error:

import numba
import numpy as np
from numba import types
from numpy import zeros_like, isfinite
from numpy.linalg import solve
from numpy.random import uniform


@numba.njit(parallel=True)
def foo(A_, b_, M1=None, M2=None):
    x_ = zeros_like(b_)
    r = b_ - A_.dot(x_)
    flag = 1

    if isinstance(M1, types.NoneType):           # Error here
        y = r
    else:
        y = solve(M1, r)
        if not isfinite(y).any():
            flag = 2

    if isinstance(M2, types.NoneType):
        z = y
    else:
        z = solve(M2, y)
        if not isfinite(z).any():
            flag = 2

    return z, flag


N = 10

tmp = np.random.rand(N, N)
A = np.dot(tmp, tmp.T)

x = np.zeros((N, 1), dtype=np.float64)
b = np.vstack([uniform(0.0, 1.0) for i in range(N)])

X_1, info = foo(A, b)

Also if I change the decorator to generated_jit() I get the following error:

r = b_ - A_.dot(x_)
AttributeError: 'Array' object has no attribute 'dot'

Answer 1

Numba compiles the function and requires every variables to be statically typed. This means that each variable has only one unique type: one variable cannot be of both the type NoneType and something else as opposed to with CPython based on dynamic typing. Dynamic typing is also a major source of the slowdown of CPython. Thus, using isinstance in nopython JITed Numba functions does not make much sense. In fact, this built-in function is not supported.

That being said, Numba supports optional arguments by specifying optional(ArgumentType) in the signature (note that the resulting type of the variable is optional(ArgumentType) and not ArgumentType nor NoneType. You can then test if the argument is set using if yourArgument is None:. I do not know what is the type of M1 and M2 in your code but they need to be explicitly defined in the signature with optional argument.