def div_safe( numerator, denominator ):
    """
    Ufunc-extension that returns 0 instead of nan when dividing numpy arrays

    Parameters
    ----------
    numerator: array-like

    denominator: scalar or array-like that can be validly divided by the numerator

    returns a numpy array

    example: div_safe( [-1, 0, 1], 0 ) == [0, 0, 0]
    """
    #First handle scalars
    if np.isscalar(numerator):
        raise ValueError("div_safe should only be used with an array-like numerator")

    #Then numpy arrays
    try:
        with np.errstate(divide='ignore', invalid='ignore'):
            result = np.true_divide( numerator, denominator )
            result[ ~ np.isfinite( result )] = 0  # -inf inf NaN
        return result
    except ValueError as e:
        raise e