Calling pointpaths.skyum raises NameError if the user does not have Numba installed. This is caused by a check for Numba in centrography.py on lines 402-405

try:
    from numba import njit, boolean

    HAS_NUMBA = True

which, if the numba import fails, leaves HAS_NUMBA undefined.

Suggested fix: define HAS_NUMBA = False in the except ModuleNotFoundError statement that begins on line 445.