While Python has arbitrary-sized integers, integers in Numba-compiled functions get a fixed size (either through type inference, or from an explicit specification by the user). This means that arithmetic operations can wrapround or produce undefined results or overflow.
In nopython mode, global and closure variables are frozen by Numba: a Numba-compiled function sees the value of those variables at the time the function was compiled. Also, it is not possible to change their values from the function.
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