在python中使用正则表达式开始字符

Question

I'm trying to implement regular expressions in python so that I will only print part of a string and not a whole string. I'm trying to print the characters that are numbers and also precede the letter characters of this string. I'm getting an error with the beginning of string character here

Heres my code import re

var = "20cw"
var2 = re.compile(^[0-9]?[0-9], var)
print var2

Here is the error I'm getting

  File "./temp.py", line 5
    var2 = re.compile(^[0-9]?[0-9], var)
                      ^
SyntaxError: invalid syntax

Expected output is

20

Answer 1

将正则表达式用字符串括起来（带引号）：

var2 = re.findall('^\d{2}', var)