Python正则表达式匹配HTML页面编码

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=["']"']"']"']"


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'