一、判断正负符号
二、逐字转值(是否为数字,ascii码转值)
三、越界判断
import sys
max_int = sys.maxsize
num_tuple = ('0', '1', '2', '3', '4', '5', '6', '7', '8', '9')def _int(input_string):
total_num = 0
is_minus = False
string = input_string.strip()
if string.startswith('-'):is_minus = True
string = string[1:]for s in string:
if s not in num_tuple:
print("input error")
return 0num = ord(s) - ord('0')
total_num = total_num * 10 + num
if total_num > max_int:total_num = max_int
breakreturn total_num * -1 if is_minus else total_num