Longest Non Repeating Substring

file.py

s = "abcabcbb"
t = []
c = 0
n = 0
for i in s:
  if i in t:
    if c > n:
      n = c
      c = 0
      t = [i]
      if len(s) < 2 * len(t):
        break
  else:
    t.append(i)
    c = len(t)
print(n)