如何提取具有前导字符和值单位的数字？

^([a-zA-Z]+)?(\d+(\.\d+)?)\s*([a-zA-Z]+)?$

import re

def extract_number_with_unit(string):
    pattern = r'^([a-zA-Z]+)?(\d+(\.\d+)?)\s*([a-zA-Z]+)?$'
    match = re.match(pattern, string)
    if match:
        groups = match.groups()
        leading_chars = groups[0]
        value = groups[1]
        unit = groups[3]
        return leading_chars, value, unit
    else:
        return None

# 示例用法
string = "USD 100"
result = extract_number_with_unit(string)
if result:
    leading_chars, value, unit = result
    print("前导字符:", leading_chars)
    print("数值:", value)
    print("单位:", unit)
else:
    print("未找到匹配的数字")

前导字符: USD
数值: 100
单位: None