python：对list去重

numbers = [1,7,3,2,5,6,2,3,4,1,5]
new_numbers = list(set(numbers))
print new_numbers

numbers = [1,7,3,2,5,6,2,3,4,1,5]
new_numbers = []
for x in numbers:
    if x not in new_numbers:
       new_numbers.append(x)
print(new_numbers)

numbers = [1,7,3,2,5,6,2,3,4,1,5]
new_numbers = list(set(numbers))
new_numbers.sort(key=numbers.index)
print(new_numbers)