我正在我的web应用程序中实现一些错误处理：

import parse

try:
    cursor.execute("INSERT INTO User (email, name, hash) VALUES ('%s', '%s', '%s');" % (email, name, pw_hash))
except MySQLdb.IntegrityError as e:
    msg = e.args[1]
    print(email)
    print(e)
    if "Duplicate entry" in msg: 
        fields = parse("Duplicate entry '{}' for key '{}'", msg)
        msg = "%s %s already exists." % (fields[1], fields[0])
        raise ConflictException(msg) //sends response to client with status code 409

问题是，异常不包括导致错误的整个输入字符串。当我测试重复的电子邮件时，我会生成一个合理有效的电子邮件，当mysql尝试插入已经存在的电子邮件时 IntegrityError 升起。
当我打印错误与输入电子邮件时，错误中的电子邮件已被截断：
实际输入电子邮件：

a+EMCayiy_O+xGVcYZxvZqHZTMv9-6aE2qSElp7LHQIdcmLMKbvlXo89nrUNsIFbplm36lVmQRvjzABDhGVab_LLvWQLDkyoMJakzb8FcacHnNgj642jLhbu5imT+ENxR01W-DcWTJdZPRo0V155UW@PakZ7hfY2I953-4ackKNoNrJbcHkcwNGruEvprdAFgz2xpVvTbzt0LMxHZEgNYuA641Uj9AA1zC39B6C.VzCgqPzPj09bSqDyPNjDuZR

数据库引发的错误：

(1062, "Duplicate entry 'a+EMCayiy_O+xGVcYZxvZqHZTMv9-6aE2qSElp7LHQIdcmLMKbvlXo89nrUNsIFb' for key 'email'")

因此，我的测试失败了：

def assert_register_fail(self, email, name, password, confirmed_password, expected_msg, expected_code):
    response = self.register(email, name, password, confirmed_password)
    res = json.loads(response.data.decode())
    self.assertEqual(response.status_code, expected_code)
    self.assertEqual(res["message"], expected_msg)

def test_email_taken(self):
    email = self.gen_email()
    password = self.gen_pass()
    expected_msg = "email %s already exists." % email
    self.assert_register_success(email, self.gen_name(), password, password)
    self.assert_register_fail(email, self.gen_name(), password, password, expected_msg, 409)

测试显然希望整个无效电子邮件都包含在错误消息中：

AssertionError: 'emai[61 chars]5YD.q already exists.' != 'emai[61 chars]5YD.qq5Po.OYDxtaL-UcMDYx4Uw5aEth-+GWeMJrSat_fH[162 chars]sts.'
- email Jf5QbVi+l1x3VOrYYc5c-wlgg+s7b4TOHVQqHwtIT+rouTe1CQShWlX384d5YD.q already exists.
+ email Jf5QbVi+l1x3VOrYYc5c-wlgg+s7b4TOHVQqHwtIT+rouTe1CQShWlX384d5YD.qq5Po.OYDxtaL-UcMDYx4Uw5aEth-+GWeMJrSat_fHF6THMOwBOawCZo1Vu8.hJoWvH.l.LUYNwANrtgAy+vM.h@W884ZKLYhgknKSeDSCQxC9lLUYa3KSVXNKPUWxIyNXyK9De-FN-t935GBb3ma6b2wWel-L4xL2zM3Y6M.Qy5g3O-i2SMiE7PpsdALSUs already exists.

我可以完全用另一种方法把一些东西拼凑在一起，但我不认为这样会更好。
另外，我可以将生成的电子邮件长度限制在60个字符左右，mysql不会在这一点上截断。这些测试将通过，但它们可能无法反映真实世界的情况。
那么，如何从mysql中检索导致错误的整个参数呢？