python 列表，元组，字符串 进行 切片操作时 超出索引值不报错 返回对应类型的空值！！！

c = 'a'
d = c[:2]
print(d)
e = c[2:]
print(type(e))
try:
    f = int(c[3:])
except:
    f = 0
print(f)
print(type(f))