Index out of range when it should not

Question

Hello guys im learning python and im trying to make a string that concentrates binary numbers together baseed on similarity from a list .. so ['1','0','0','0','0','1','1'] becomes '1 0000 11' .. I wrote something and ive been staring at the screen for an hour trying to find the mistake i made ., anyone have any idea why is s[i]+1 giving me an out of index error when it should not be entered anyway ? .

s=['1','1','0','0','0','0','1']
for i in range(len(s)) :
    u=''
    if i <= (len(s)-1):
        if s[i]==s[i+1]:
            u+=s[i]
        elif s[i] != s[i+1]:
            u+=(s[i]+' ')
    elif i==len(s):
        u+=s[i]

Answer 1

s=['1','1','0','0','0','0','1']
print("LENGTH: " + str(len(s)))
u=''
for i in range(len(s)) :
    if i < len(s) - 1:
        if s[i]==s[i+1]:
            u+=s[i]
        elif s[i] != s[i+1]:
            u+=(s[i]+' ')
    else:
        u+=s[i]
print(u)

IIUC, with some minor changes, this does what you want.

output: 11 0000 1