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" />'
   ]



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'