Python正则表达式匹配HTML页面编码

html页面一般都会指定一个编码，如何获取到是处理html页面的第一步，因为错误的编码必然带来后面处理的问题。这里我用python的正则表达式写了个：

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'