How to use the tilecloud.lib.s3.HeaderDict function in tilecloud

def sign(self, method, bucket_name=None, url=None, headers=None,
             sub_resources=None):
        headers = HeaderDict() if headers is None else headers.copy()
        string_to_sign = []
        string_to_sign.append('{0!s}\n'.format(method))
        string_to_sign.append('{0!s}\n'.format(headers.get('content-md5', ('',))))
        string_to_sign.append('{0!s}\n'.format(headers.get('content-type', ('',))))
        if 'x-amz-date' in headers:
            string_to_sign.append('\n')
        else:
            string_to_sign.append('{0!s}\n'.format(headers.get('date', ('',))))
        for key in sorted(set(imap(str.lower, headers.keys())) - self.SIGN_IGNORE_HEADERS):
            string_to_sign.append('{0!s}:{1!s}\n'.format(key, headers[key]))
        if bucket_name is not None:
            string_to_sign.append('/{0!s}'.format(bucket_name))
        if url is not None:
            string_to_sign.append(urlparse(url).path)
        if sub_resources:
            query_params = []

headers['x-amz-date'] = \
                datetime.utcnow().strftime('%a, %d %b %Y %H:%M:%S +0000')
        if self.iam_token is not None:
            self._refresh_iam_credentials()
            headers['x-amz-security-token'] = self.iam_token
        headers['Authorization'] = self.sign(method, bucket_name, url, headers,
                                             sub_resources)
        while True:
            try:
                if self.connection is None:
                    self.connection = httplib.HTTPConnection(self.host)
                self.connection.request(method, url, body, headers)
                response = self.connection.getresponse()
                if response.status not in xrange(200, 300):
                    raise S3Error(method, url, body, headers, response)
                headers = HeaderDict(response.getheaders())
                body = response.read()
                return (headers, body)
            except httplib.BadStatusLine as exc:
                logger.warn(exc)
                self.connection = None
            except httplib.CannotSendRequest as exc:
                logger.warn(exc)
                self.connection = None
            except ssl.SSLError as exc:
                logger.warn(exc)
                self.connection = None
            except IOError as exc:
                if exc.errno == errno.ECONNRESET:
                    logger.warn(exc)
                    self.connection = None
                else:

def request(self, method, bucket_name=None, url=None, headers=None,
                body=None, sub_resources=None):
        headers = HeaderDict() if headers is None else headers.copy()
        if 'x-amz-date' not in headers:
            headers['x-amz-date'] = \
                datetime.utcnow().strftime('%a, %d %b %Y %H:%M:%S +0000')
        if self.iam_token is not None:
            self._refresh_iam_credentials()
            headers['x-amz-security-token'] = self.iam_token
        headers['Authorization'] = self.sign(method, bucket_name, url, headers,
                                             sub_resources)
        while True:
            try:
                if self.connection is None:
                    self.connection = httplib.HTTPConnection(self.host)
                self.connection.request(method, url, body, headers)
                response = self.connection.getresponse()
                if response.status not in xrange(200, 300):
                    raise S3Error(method, url, body, headers, response)

def put(self, bucket_name=None, url=None, headers=None, body=None):
        headers = HeaderDict() if headers is None else headers.copy()
        if 'Content-MD5' not in headers:
            headers['Content-MD5'] = b64encode(hashlib.md5(body).digest())
        return self.request('PUT', bucket_name, url, body=body, headers=headers)