some experimentation with pyright

pyright_conditional.py

# https://github.com/microsoft/pyright/issues/219
def test_conditional(
    z: str | bool,
) -> None:
    z_is_stringy = isinstance(z, str)

    if z_is_stringy:
        z_upper = z.upper()

    if z_is_stringy:
        N = len(z_upper)

pyright_narrowing.py

from __future__ import annotations
from typing import cast, Any

def apply_color_scale_limits(
    data_array: list[int] | None = None,
) -> None:

    if data_array is None:
        default_value = get_list_as_any()
        cast_value = cast(list[int], default_value)
        data_array = default_value
        reveal_type(default_value)
        reveal_type(cast_value)
        reveal_type(data_array)

    reveal_type(data_array)


def get_list_as_any() -> Any:
    return [1,2,3]

pyright_numpy.py

import numpy as np
import numpy.typing as npt
def _on_rectilinear_grid_except_nan(x_data: npt.NDArray[np.floating], y_data: npt.NDArray[np.floating]) -> bool:
    """
    check that data is on a rectilinear grid. e.g. all points are the same as the  first
    row and column with the exception of nans. Those represent points not yet measured.
    """
    x_row = x_data[:, 0:1]
    y_row = y_data[0:1, :]
    return (
        np.nanmax(np.abs(x_data - x_row)) == 0
        and np.nanmax(np.abs(y_data - y_row)) == 0
    )