The below code causes an error with Numba. The issue appears to be around the variables PV and V, i.e. if we comment out line 70 the error does not occur. This code is a minimal complete example of the issue that is occuring when executing a larger Python file from which this code was extracted.

numba_error_gist.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)