code: def _dnsname_match(dn, hostname, max_wildcards=1):
      
      pats = []
      if not dn:
          return False
  
      split_dn = dn.split(r'.')
      leftmost, remainder = split_dn[0], split_dn[1:]
  
      wildcards = leftmost.count('*')
      if wildcards > max_wildcards:
          # Issue #17980: avoid denials of service by refusing more
          # than one wildcard per fragment.  A survey of established
          # policy among SSL implementations showed it to be a
          # reasonable choice.
          raise CertificateError(
              "too many wildcards in certificate DNS name: " + repr(dn))
  
      # speed up common case w/o wildcards
      if not wildcards:
          return dn.lower() == hostname.lower()
  
      # RFC 6125, section 6.4.3, subitem 1.
      # The client SHOULD NOT attempt to match a presented identifier in which
      # the wildcard character comprises a label other than the left-most label.
      if leftmost == '*':
          # When '*' is a fragment by itself, it matches a non-empty dotless
          # fragment.
          pats.append('[^.]+')
      elif leftmost.startswith('xn--') or hostname.startswith('xn--'):
          # RFC 6125, section 6.4.3, subitem 3.
          # The client SHOULD NOT attempt to match a presented identifier
          # where the wildcard character is embedded within an A-label or
          # U-label of an internationalized domain name.
          pats.append(re.escape(leftmost))
      else:
          # Otherwise, '*' matches any dotless string, e.g. www*
          pats.append(re.escape(leftmost).replace(r'\*', '[^.]*'))
  
      # add the remaining fragments, ignore any wildcards
      for frag in remainder:
          pats.append(re.escape(frag))
  
      pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
      return pat.match(hostname)
docs: Matching according to RFC 6125, section 6.4.3
  
      http://tools.ietf.org/html/rfc6125#section-6.4.3