剑指offer-表示数值的字符串-python

题目描述
请实现一个函数用来判断字符串是否表示数值（包括整数和小数）。例如，字符串"+100",“5e2”,"-123",“3.1416"和”-1E-16"都表示数值。 但是"12e",“1a3.14”,“1.2.3”,"±5"和"12e+4.3"都不是。

# -*- coding:utf-8 -*-
class Solution:
    # s字符串
    def isNumeric(self, s):
        # write code here
        if len(s)==1 and '0'<=s<='9':
            return True
        if not('1'<=s[0]<='9' or s[0] in {'+','-'}):
            return False
        point_flag = 0 #为1则不允许再出现.
        allow_sign = 0 
        e_flag = 0 # 为1则不允许再出现e/E
        for idx in range(1,len(s)):
            # e/E 后面允许出现一个正负号
            if allow_sign == 1 and s[idx] in {'+','-'}:
                allow_sign = 0
                continue
            if '0'<=s[idx]<='9':
                continue
            elif s[idx] == '.' and point_flag == 0:
                point_flag = 1 
            elif (s[idx] == 'e' or s[idx]=='E') and e_flag == 0 and idx<len(s)-1:
                if '1'<=s[idx-1]<='9':
                    allow_sign = 1
                    e_flag = 1
                    # e后面跟的数值不能带.
                    point_flag = 1
            else:
                return False
        return True