String to Integer (atoi)

atoi.py

class Solution(object):
    def myAtoi(self, str):
        """
        :type str: str
        :rtype: int
        """
        
        def in_range(num):
            if num > 2 ** 31 - 1: return 2 ** 31 - 1
            if num < -2**31: return -2**31
            else: return num
        
        #define state transition tables
        states = {
            # State (1) - initial state
            1: { 'blank': 1, 'sign': 2, 'digit': 3 },
            # State (2) - Signed - after finding +, -
            2: { 'digit': 3 },
            # State (3) - Integer
            3: { 'digit': 3 },
        }
        
        # begin with initial state
        current_state = 1
        val = 0
        sign = 1
        for c in str:
            if c == ' ':
                c_type = 'blank'
            elif c in '+-':
                c_type = 'sign'
            elif c in '0123456789':
                c_type = 'digit'
            else:
                c_type = 'else'
            
            # if we can not move on, we end it here
            if c_type not in states[current_state]:
                break
            
            # process number
            if c_type == 'sign':
                sign = 1 if c == '+' else -1
            elif c_type == 'digit':
                val = val * 10 + int(c)
            
            # move to next state
            current_state = states[current_state][c_type]

        return in_range(sign * val)