The below code causes an error with Numba. The stack trace is as follows:

palmer_numba_error_example.py

import numba
import numpy as np

@numba.jit
def _pdsi_from_zindex(Z):

    ## INITIALIZE PDSI AND PHDI CALCULATIONS
    
    # V is the sum of the Uw (Ud) values for the current and previous months of an
    # established dry (wet) spell and is used in calculating the Pe value for a month.
    V = 0.0
    Pe = 0.0 # the probability that the current wet or dry spell has ended in a month
    X1 = 0.0 # the severity index value for an incipient wet spell for a month
    X2 = 0.0 # the severity index value for an incipient dry spell for a month
    X3 = 0.0 # the severity index value of the current established wet or dry spell for a month
    
    number_of_months = Z.shape[0]
    
    # initialize arrays
    PX1 = np.zeros((number_of_months,))
    PX2 = np.zeros((number_of_months,))
    PX3 = np.zeros((number_of_months,))
    PPe = np.zeros((number_of_months,))
    X = np.zeros((number_of_months,))
    PMDI = np.zeros((number_of_months,))
    
    # loop over all months in the dataset, calculating PDSI and PHDI for each
    for k in range(number_of_months):
        
        pass
    
        if (Pe == 100) or (Pe == 0):   # no abatement underway
            
            if abs(X3) <= 0.5:   # drought or wet spell ends

                # PV is the preliminary V value and is used in operational calculations.
                PV = 0 
                 
            elif X3 > 0.5: # Wet spell underway
                
                if Z[k] >= 0.15: # Wet spell intensifies
                
                    pass
                
                else: # Wet spell starts to abate, and it may end.
                
                    pass
                                                                                               
            elif X3 < -0.5: # Drought underway
                
                if Z[k] <= -0.15: # Drought intensifies 
                
                    pass
                
                else: # Drought starts to abate, and it may end.
                
                    pass
                                                                                          
        else: # Abatement underway
            
            if X3 > 0: # Wet spell underway
                
                pass
            
            else: # Drought underway
                
                pass

        ## Assign V, Pe, X1, X2, and X3 for use with the next month
        V = PV
        Pe = PPe[k]
        X1 = PX1[k]
        X2 = PX2[k]
        X3 = PX3[k]
        
        # round values to four decimal places
        for values in [X1, X2, X3, Pe, V, X, PX1, PX2, PX3, PPe]:
            values = np.around(values, decimals=4)
        
    # return the computed variables
    return X, PMDI

#-----------------------------------------------------------------------------------------------------------------------
if __name__ == '__main__':
 
    z = np.array([
        -1.020,  1.631, -0.828,  1.453,  0.802, -8.602,  0.291,  0.476,  0.226,  1.368,  0.415, -0.219,  \
         0.856, -0.302, -0.738, -0.703, -0.040,  8.376, -0.183, -1.259,  0.575, -1.228,  0.569,  0.011,  \
        -0.029,  0.975, -1.302,  0.602, -0.698,  0.716,  2.791, -2.360,  2.602,  0.977, -0.908,  0.132])
    _pdsi_from_zindex(z)