The Python regular expression matches the HTML page encoding

The html page generally specifies an encoding, and how to get it is the first step in handling the html page, because the wrong encoding inevitably leads to the following problems. Here I wrote a regular expression in python:

import re

a = ["<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />",
   '<meta http-equiv=Content-Type content="text/html;charset=gb2312">',
   '<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">',
   '<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />',
   '<meta http-equiv="content-type" content="text/html; charset=utf-8" />',
   '<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />',
   '<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />'
   ]



b = "<meta[ ]+http-equiv=["']?content-type["']?[ ]+content=["']?text/html;[ ]*charset=([0-9-a-zA-Z]+)["']?"


B = re.compile(b, re.IGNORECASE)


for ax in a:
  r1 = B.search(ax)

  if r1:
    print r1.group()
    print r1.group(1), len(r1.group())
  else:
    print 'not match'