如何根据点获取字符串的子项

string = "这是一个字符串"
start = 2
end = 4

substring = string[start:end]
print(substring)

是一

import re

string = "这是一个字符串"
start = 2
end = 4

pattern = r"^.{%s}(.{%s}).*" % (start, end - start)
substring = re.search(pattern, string).group(1)
print(substring)

是一