'NoneType' object has no attribute 'args'

[nishio]

Reporting a bug

• I am using the latest released version of Numba (most recent is visible in
  the change log (https://github.com/numba/numba/blob/master/CHANGE_LOG).
• I have included below a minimal working reproducer (if you are unsure how
  to write one see http://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports).

The following code:

from numba.pycc import CC


def main():
    ds = {1: (2, 3)}       # (A)
    x = ds.get(1, (4, 5))  # (B)
    # x = ds[1]            # (B2)
    y = x[1]               # (C)


cc = CC('my_module')
cc.export('main', '()')(main)
cc.compile()

produces the following error(digested):

numba.core.errors.LoweringError: Failed in nopython mode pipeline (step: nopython mode backend)
'NoneType' object has no attribute 'args'

File "t2.py", line 8:
def main():
    <source elided>
    # x = ds[1]            # (B2)
    y = x[1]               # (C)
    ^

During: lowering "$26binary_subscr.10 = static_getitem(value=x, index=1, index_var=$const24.9)" at t2.py (8)

Full stderr: https://gist.github.com/nishio/99eebe8011553025726a7730d2bef61f

If I use the line B2 instead of the line B, the error doesn't occur.

[esc]

@nishio thank you for reporting this, we appreciate your input.

I can reproduce this and I can simplify this further:

from numba import njit


@njit
def main():
    ds = {1: (2, 3)}       # (A)
    x = ds.get(1, (4, 5))  # (B)
    #x = ds[1]            # (B2)
    y = x[1]               # (C)
    return y


print(main())

[esc]

It does seem to work fine in the interpreter:

In [1]: from numba.typed import Dict
d
In [2]: d = Dict()

In [3]: d[1] = (2, 3)

In [4]: d.get(1, (4,5))
Out[4]: (2, 3)

In [5]: d.get(2, (4,5))
Out[5]: (4, 5)

Also, here is a more verbose reproducer that highlights the issue:

from numba import njit
from numba.typed import Dict


@njit
def foo(d):
    return d.get(1, (4, 5))


@njit
def bar(d):
    return d.get(1, (4, 5))[1]


d = Dict()
d[1] = (2, 3)

print(foo.py_func(d))
print(foo(d))

print(bar.py_func(d))
print(bar(d))

As you can see, the error occurs when we attempt to index into the tuple returned by get.

So, the problem is probably that get returns an OptionalType and that we then fail to index into that. Which is also what the error message here alludes to:

NotImplementedError: No definition for lowering static_getitem(OptionalType(UniTuple(int64 x 2)), Literal[int](1)) -> int64

[esc]

It may be possible to check that get does have a default in this case and therefore we can return a non-Optional type.