python - append to a sublist appends to every sublist

Question

I'm writing a simple hash table with a set of 10 bucket lists. The index is calculated using the built-in hash() and then modulo the table size. However, when I try to append the object to the bucket list at that index, it gets appended to every bucket list instead. I've tried defining add_HT different ways but i keep getting the same result. What am I doing wrong?

size = 10
HT = [ [] ] * size

def add_HT(data):
    index = hash(data) % size
    HT[index].append(data)

print HT

[[], [], [], [], [], [], [], [], [], []]

add_HT('hello')

[['hello'], ['hello'], ['hello'], ['hello'], ['hello'], ['hello'], ['hello'], ['hello'], ['hello'], ['hello']]

Answer 1

HT = [ [] ] * size makes size number of pointers to the same list. add_HT isn't the problem here. You need to define HT as [[] for i in xrange(size)].