Using OrderedDict and json.dumps Separators to Generate Consistent MD5 Signatures for Python ERP API Integration

When integrating a Python application with the Guanyiyun ERP system, the required request payload includes a signature that is computed by concatenating a secret string before and after the JSON representation of the data and then applying an MD5 hash (uppercase 32‑character). The original PHP example works because the associative array preserves order, but Python's built‑in dict is unordered, causing the JSON string (and thus the MD5) to change on each run.

The solution is to use collections.OrderedDict to keep the key order consistent and to call json.dumps with the separators=(',' , ':') argument, which removes the space after commas that would otherwise alter the hash.

Example code:

def getShops():
    data = OrderedDict()
    data["appkey"] = appkey
    data["sessionkey"] = sessionkey
    data["method"] = method
    data["page_no"] = "1"
    data["page_size"] = "10"
    data["sign"] = sign(data, secret)
    response = requests.post(url=url, data=json.dumps(data))
    print(response.text)

def sign(data, secret):
    json_str = json.dumps(data, separators=(",", ":"))
    full_str = secret + json_str + secret
    sign_code = hashlib.md5(full_str.encode("utf-8")).hexdigest().upper()
    return sign_code

By assembling the payload with an OrderedDict and serializing it without extra spaces, the generated MD5 signature matches the ERP's expectations, eliminating the frequent errors previously encountered.