RandomizedSeclect in Python

def MyPartition(a,p,r):
    x = a[r]
    i = p-1
    for j in range(p,r):
        if a[j]<=x:
            i=i+1
            a[i],a[j] = a[j],a[i]
    a[i+1],a[r] = a[r],a[i+1]
    return i+1

def MyRandomizedPartition(a,p,r):
    if p>r:
        print 'p must be smaller than r!'
        return
    import random
    k = int(random.random()*(r-p+1)+p)
    a[k],a[r] = a[r],a[k]
    return MyPartition(a,p,r)

def MyRandomizedSelect(a,p,r,i):
    if p==r:
        return a[p]
    q = MyRandomizedPartition(a,p,r)
    k = q-p+1
    if i==k:
        return a[q]
    elif i<k:
        return MyRandomizedSelect(a,p,q-1,i)
    else:
        return MyRandomizedSelect(a,q+1,r,i-k)