To count all occurrences of 'A' in a list, we can use S.count('A').
To determine whether there are at most 2 consecutive L's, we can search for 'LLL'. If a string has 3 or more consecutive L's, it will definitely contain 'LLL'.
Alternatively, we could look at
S[i:i+3] for 'LLL', or we could look at groups
len(list(v)) >= 3 for k, v in itertools.groupby(S) if k == 'L'.
def checkRecord(self, S): return S.count('A') <= 1 and 'LLL' not in S