如何在Python中正确序列化和反序列化分页大小？

在我的

Python

应用程序中，我对

Cassandra

数据库进行查询。我正在尝试通过包实现分页。从下面的代码可以看出，

paging_state

返回

字节

数据类型。我可以将此值转换为

字符串

数据类型。然后我将

str\u paging\u state

变量的值发送给客户端。如果此客户端再次向我发送

str\u paging\u state

，我希望在查询中使用它

这部分代码的作用是：

query = "select * from users where user_type = 'clients';"
statement = SimpleStatement(query, fetch_size=10)
results = session.execute(statement)

paging_state = results.paging_state
print(type(paging_state)) # <class 'bytes'>

str_paging_state = str(paging_state)
print(str_paging_state) # "b'\\x00C\\x00\\x00\\x00\\x02\\x00\\x00\\x00\\x03_hk\\x00\\x00\\x00\\x11P]5C#\\x8bGD~\\x8b\\xc7g\\xda\\xe5rH\\xb0\\x00\\x00\\x00\\x03_rk\\x00\\x00\\x00\\x18\\xee\\x14\\xf7\\x83\\x84\\x00tTmw[\\x00\\xec\\xdb\\x9b\\xa9\\xfd\\x00\\xb9\\xff\\xff\\xff\\xff\\xfe\\x01\\x00'"

错误：

[ERROR] NoHostAvailable: ('Unable to complete the operation against any hosts')
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 51, in lambda_handler
    results = cassandra_connection.execute(statement, paging_state=bytes(paging_state.encode()))
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 2618, in execute
    return self.execute_async(query, parameters, trace, custom_payload, timeout, execution_profile, paging_state, host, execute_as).result()
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 4877, in result
    raise self._final_exceptionEND RequestId: 4b7bf588-a2d2-45e5-ad7e-8611f1704313

[ERROR] ProtocolException: <Error from server: code=000a [Protocol error] message="Invalid value for the paging state">
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 50, in lambda_handler
    results = cassandra_connection.execute(
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 2618, in execute
    return self.execute_async(query, parameters, trace, custom_payload, timeout, execution_profile, paging_state, host, execute_as).result()
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 4877, in result
    raise self._final_exceptionEND RequestId: 979f098a-a566-4904-821a-2ce06522d909

在Java中，我找到了

.fromString

方法，该方法从先前使用

toString（）

生成的字符串创建

PagingState

对象。不幸的是，我没有在Python中找到此方法的等效项

我还尝试使用package对

分页状态

进行解码和编码

str_paging_state = codecs.decode(paging_state, encoding='utf-8', errors='ignore')
# "\u0000C\u0000\u0000\u0000\u0002\u0000\u0000\u0000\u0003_hk\u0000\u0000\u0000\u0011P]5C#GD~grH\u0000\u0000\u0000\u0003_rk\u0000\u0000\u0000\u0018\u0014\u0000tTmw[\u0000ۛ\u0000\u0001\u0000"

# Raise error
results = session.execute(statement, paging_state=codecs.encode(str_paging_state, encoding='utf-8', errors='ignore'))

在这种情况下，我看到下一个错误：

[ERROR] NoHostAvailable: ('Unable to complete the operation against any hosts')
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 51, in lambda_handler
    results = cassandra_connection.execute(statement, paging_state=bytes(paging_state.encode()))
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 2618, in execute
    return self.execute_async(query, parameters, trace, custom_payload, timeout, execution_profile, paging_state, host, execute_as).result()
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 4877, in result
    raise self._final_exceptionEND RequestId: 4b7bf588-a2d2-45e5-ad7e-8611f1704313

[ERROR] ProtocolException: <Error from server: code=000a [Protocol error] message="Invalid value for the paging state">
Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 50, in lambda_handler
    results = cassandra_connection.execute(
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 2618, in execute
    return self.execute_async(query, parameters, trace, custom_payload, timeout, execution_profile, paging_state, host, execute_as).result()
  File "/opt/python/lib/python3.8/site-packages/cassandra/cluster.py", line 4877, in result
    raise self._final_exceptionEND RequestId: 979f098a-a566-4904-821a-2ce06522d909

---

我将感谢任何帮助

只需将二进制数据转换为十六进制字符串或base64即可-用于此。例如，对于第一种情况的函数hexlify/unhexlify（或在Python 3中使用二进制数据的

.hex

方法），对于base64-使用函数

b2a\U base64

/

a2b\U base64

谢谢您的回答！我测试了它们。我可以说，

hexlify

、

unexlify

和

a2b_base64

函数工作没有任何问题。但功能有问题。在我的例子中，函数只在没有

星号字符

和

换行符

选项的情况下工作。十六进制是最稳定的，base64+HTTP可能会中断某些字符。。。