[INST] Implement merge sort in python/n [/INST]  ###Response: Here is the implementation of Merge Sort in Python:

```
# Merge Sort Algorithm

def mergeSort(arr):
    if len(arr) > 1:

        mid = len(arr) // 2
        L = arr[:mid]
        R = arr[mid:]

        mergeSort(L)
        mergeSort(R)

        i = j = k = 0

        while i < len(L) and j < len(R):
            if L[i] < R[j]:
                arr[k] = L[i]
                i += 1
            else:
                arr[k] = R[j]
                j += 1
            k += 1

        while i < len(L):
            arr[k] = L[i]
            i += 1
            k += 1

        while j < len(R):
            arr[k] = R[j]
            j += 1
            k += 1

# Driver Code
arr = [12, 11, 13, 5, 6, 7]
mergeSort(arr)
print("Sorted array is:", arr)

```
In this implementation, the `mergeSort()` function is recursively called on the left and right halves of the input array until the length of each sub-array is 1 or less. The actual sorting is done in the `merge()` function where the two sub-arrays are combined in a sorted order. Finally, the sorted array is returned.