How to check if there is a repeated value in a list and get that value

Question

How can I find the repeated value in a list? There will always be only one repeated value

for example:

numbers=[1,2,3,4,5,3]

I need to get the value 3

This is what I was trying but it is sometimes printing the value of the same list 2 times.

endLoop=False
    for n1 in range(0,len(numbers)):
        for n2 in range(1,len(numbers)):
            if numbers[n1]==numbers[n2]:
                print numbers
                print numbers[n1]
                endLoop=True
        if endLoop:
            break

Answer 1

Keep track of numbers you have seen with a set() object, the first number that is already in the set is repeated:

def find_repeat(numbers):
    seen = set()
    for num in numbers:
        if num in seen:
            return num
        seen.add(num)

This is an efficient method to find the first repeated value, as it won't have to look at the rest of the numbers once it finds it.