代码举例：
import re
expression = "Price: $12,345.67"
# 数字放在括号中，以便能使用`group`将其提取出来，
pattern = 'Price: $([0-9,]+.[0-9]+)'
matches = re.search(pattern, expression)
entire_match = matches.group(0)
print(entire_match)
price = matches.group(1)
print("price_in_string: ", price)
# 如果字符串中存在逗号，需要将其删除，否则python无法将其转换成数字
print("price_in_float * 10 = ", float(price.replace(',', '')) * 10)
输出如下：
Price: $12,345.67 price_in_string: 12,345.67 price_in_float * 10 = 123456.7
