ECE592 Project 1 combination (1,2,3) optimized mergesort

import numpy as np

# function to merge sorted subarrays in place
def mergesort(X, p, q):

    global a
    N = q - p + 1
    if N < 2:
        return
    elif N == 2:
        if X[p] > X[q]:
            tmp = X[p]
            X[p] = X[q]
            X[q] = tmp
        return
    elif N == 3:
        if X[p+1] > X[p+2]:
            tmp = X[p+1]
            X[p+1] = X[p+2]
            X[p+2] = tmp
        if X[p] > X[p+2]:
            tmp = X[p]
            X[p] = X[p+2]
            X[p+2] = tmp
        if X[p] > X[p+1]:
            tmp = X[p]
            X[p] = X[p+1]
            X[p+1] = tmp
        return
    elif N == 4:
        if X[p] > X[p+1]:
            tmp = X[p]
            X[p] = X[p+1]
            X[p+1] = tmp
        if X[p+2] > X[p+3]:
            tmp = X[p+2]
            X[p+2] = X[p+3]
            X[p+3] = tmp
        if X[p] > X[p+2]:
            tmp = X[p]
            X[p] = X[p+2]
            X[p+2] = tmp
        if X[p+1] > X[p+3]:
            tmp = X[p+1]
            X[p+1] = X[p+3]
            X[p+3] = tmp
        if X[p+1] > X[p+2]:
            tmp = X[p+1]
            X[p+1] = X[p+2]
            X[p+2] = tmp
        return

    else:
        mergesort(X, p, p + int(N/2) - 1) #sort first half
        mergesort(X, p + int(N/2), q) # second half
        r = q
        q = p + int(N/2)
        N1 = q - p
        N2 = r - q + 1

        N1 = q - p
        N2 = r - q + 1
        currN = N1 + N2
        ind1 = 0
        ind2 = 0
        indX = p
        left = [0] * N1
        right = [0] * N2
        left[0:N1] = X[p:p+N1]
        right[0:N2] = X[q:q+N2]
        if(X[q-1]<=X[q]):
            return

        while ind1 < N1 and ind2 < N2:
            if left[ind1] > right[ind2]:
                X[indX] = right[ind2]
                ind2 += 1
            else:
                X[indX] = left[ind1]
                ind1 += 1
            indX += 1

        while ind1 < N1:
            X[indX] = left[ind1]
            ind1 += 1
            indX += 1

        while ind2 < N2:
            X[indX] = right[ind2]
            ind2 += 1
            indX += 1

    a = X

# driver code
a = np.random.randint(10000, size=10000000)
mergesort(a, 0, len(a)-1)
print(a)