def get_single_header(headers, key):
raw_headers = headers.getRawHeaders(key)<EOL>if raw_headers is None:<EOL><INDENT>return None<EOL><DEDENT>header, _ = cgi.parse_header(raw_headers[-<NUM_LIT:1>])<EOL>return header<EOL>
Get a single value for the given key out of the given set of headers.

:param twisted.web.http_headers.Headers headers:
    The set of headers in which to look for the header value
:param str key:
    The header key