Merge Sort algo implemented in PYTHON program

def mergeSort(alist): 
    print("Splitting ",alist) 
    if len(alist)>1: 
        mid = len(alist)//2 
        lefthalf = alist[:mid] 
        righthalf = alist[mid:] 

        mergeSort(lefthalf) 
        mergeSort(righthalf) 

        i=0 
        j=0 
        k=0 
        while i<len(lefthalf) and j<len(righthalf): 
            if lefthalf[i]<righthalf[j]: 
                alist[k]=lefthalf[i] 
                i=i+1 
            else: 
                alist[k]=righthalf[j] 
                j=j+1 
            k=k+1 

        while i<len(lefthalf): 
            alist[k]=lefthalf[i] 
            i=i+1 
            k=k+1 

        while j<len(righthalf): 
            alist[k]=righthalf[j] 
            j=j+1 
            k=k+1 
    print("Merging ",alist) 

alist = [54,26,93,17,77,31,44,55,20] 
mergeSort(alist) 
print(alist)