State machine

https://leetcode.com/problems/valid-number/discuss/360781/Python-with-state-machine-36ms

class Solution:
    def isNumber(self, s: str) -> bool:
        # states
        start       = 0
        int_sign    = 1
        integer     = 2
        point       = 3
        frac        = 4
        exp         = 5
        exp_sign    = 6
        exp_int     = 7
# inputs
        digit       = 1
        sign        = 2
        dot         = 3
        e           = 4
    def classify(c):
        if c in '0123456789': return digit
        if c == '.'         : return dot
        if c in '+-'        : return sign
        if c == 'e'         : return e
            raise ValueError
        machine = {
            start   : {sign:int_sign, digit:integer, dot:point},
            int_sign: {digit:integer, dot:point},
            integer : {digit:integer, dot:frac, e:exp},
            point   : {digit:frac},
            frac    : {digit:frac, e:exp},
            exp     : {digit:exp_int, sign:exp_sign},
            exp_sign: {digit:exp_int},
            exp_int : {digit:exp_int},
        }
        state = start
        for c in s.strip():
            try:
                state = machine[state][classify(c)]
            except: return False
        return state in [integer, frac, exp_int]