Determine the length of the longest chain consisting only of symbols A, B and C

[authera]

There's a file in which the letters A...Z are recorded. Determine the length of the longest chain consisting only of symbols A, B and C. My problem is, the code is only looking for the length of the chain consisting of the same letters. How can you fix the code?

file = open("2.txt").read().strip()
count = 1
max_count = 1
symbols = ""
for i in range(len(file)-1):
    if file[i] == file[i+1]:
        count += 1
    else:
         count = 1
    if count > max_count:
         max_count = count
         symbols = file[i]
print(symbols,max_count)

[Oba22]

Option 1 (decision in the forehead):

text = "XABXCABBBCAADBXXBAADX"
max_size = 0

size = 0

for letter in text:

if letter in 'ABC':

size += 1

else:

if max_size < size:

max_size = size
    size = 0

if max_size < size:

max_size = size
print(max_size)

Option 2 (corrected):

size, max_size = 0, 0

for letter in text:

size, max_size = (size + 1, max_size) if letter in 'ABC' else (0, size if max_size < size else max_size)
max_size = size if max_size < size else max_size

Option 3 (single):

It's really a little bit of a mess, and it works slower than the last one:

res = max(map(len, ''.join(letter if letter in 'ABC' else ' ' for letter in text)).split())

Option 3.1 (a little shorter):

res = max(map(len, ''.join((' ', letter)[letter in 'ABC'] for letter in text).split()))