怎样讲一个字符串转换为数字才安全

``` python
s1 = "1234"
print(int(s1))   ## 1234

s2 = '1234a'
#print(int(s2))   ## ValueError: invalid literal for int() with base 10: '1234a'

# 先判断数据类型
if s2.isdigit():
    print(int(s2))
else:
    print('s2不是数字，无法转换')

# 捕捉异常
try:
    print(int('223aaa'))
except Exception as e:
    print('223aaa不是数字，无法转换')
    print(e)
```