import hmac, base64, hashlib, urllib2base = 'https://.......'def makereq(key, secret, path, data):    hash_data = path + chr(0) + data    secret = base64.b64decode(secret)    sha512 = hashlib.sha512    hmac = str(hmac.new(secret, hash_data, sha512))    header = {        'User-Agent': 'My-First-test',        'Rest-Key': key,        'Rest-Sign': base64.b64encode(hmac),        'Accept-encoding': 'GZIP',        'Content-Type': 'application/x-www-form-urlencoded'    }    return urllib2.Request(base + path, data, header)錯誤：文件“ C：/Python27/btctest.py”，makereq中的第8行，hmac = str（hmac.new（secret，hash_data，sha512））UnboundLocalError：分配前已引用局部變量“ hmac”有人知道為什么嗎？謝謝