Lightstreamer SDK for Python Adapters

A Python library to write Data Adapters and Metadata Adapters for Lightstreamer Server. The adapters will run in a separate process, communicating with the Server through the Adapter Remoting Infrastructure.

Use

Install the package:

$ pip install lightstreamer-adapter

Configure Lightstreamer

1. Download and install Lightstreamer

2. Go to the adapters folder of your Lightstreamer Server installation. Create a new folder to deploy the remote adapters in, let's call it PythonAdapter

3. Create an adapters.xml file inside the PythonAdapter folder and use the following contents (this is an example configuration, you can modify it to your liking by using the generic template, https://lightstreamer.com/docs/ls-server/latest/remote_adapter_conf_template/adapters.xml or https://lightstreamer.com/docs/ls-server/latest/remote_adapter_robust_conf_template/adapters.xml, as a reference):

   <?xml version="1.0"?>
   <adapters_conf id="PROXY_PYTHON">
      <metadata_provider>
         <adapter_class>ROBUST_PROXY_FOR_REMOTE_ADAPTER</adapter_class>
         <classloader>log-enabled</classloader>
         <param name="request_reply_port">8003</param>
         <param name="timeout">36000000</param>
      </metadata_provider>
      <data_provider>
         <adapter_class>ROBUST_PROXY_FOR_REMOTE_ADAPTER</adapter_class>
         <classloader>log-enabled</classloader>
         <param name="request_reply_port">8001</param>
         <param name="timeout">36000000</param>
      </data_provider>
   </adapters_conf>

4. Take note of the ports configured in the adapters.xml file as those are needed to write the remote part of the adapters.

Write the Adapters

Create a new python module, let's call it adapters.py, where we will put the minimal logic required to write a basic Adapter Set.

1. Import the server classes needed to setup the connection to the Lightstreamer server, and the adapter classes to be extended to write your own Remote Adapters:

   from lightstreamer_adapter.server import (DataProviderServer, MetadataProviderServer)
   from lightstreamer_adapter.interfaces.data import DataProvider
   from lightstreamer_adapter.interfaces.metadata import MetadataProvider

2. Create a new Remote Data Adapter by subclassing the DataProvider abstract class:

   class MyDataAdapter(DataProvider):
       """This Remote Data Adapter sample class shows a simple implementation of
       the DataProvider abstract class."""
   
       def __init__(self):
           # Reference to the provided ItemEventListener instance
           self._listener = None
   
       def issnapshot_available(self, item_name):
           """Returns True if Snapshot information will be sent for the item_name
           item before the updates."""
           snapshot = False  # May be based on the item_name item
           return snapshot
   
       def set_listener(self, event_listener):
           """Caches the reference to the provided ItemEventListener instance."""
           self._listener = event_listener
   
       def subscribe(self, item_name):
           """Invoked to request data for an item. From now on you can start
           sending real time updates for item_name item, through invocations like
           the following:
   
           self._listener.update(item_name, {'field1': valField1,
                                             'field2': valField2}, False)
           """
   
       def unsubscribe(self, item_name):
           """Invoked to end a previous request of data for an item. From now on,
           you should stop sending updates for item_name item."""

3. Create a new Remote Metadata Adapter by subclassing the MetadataProvider class, if the latter's default behaviour does not meet your requirements, and override the methods for which you want to supply a custom implementation:

   class MyMetadataAdapter(MetadataProvider):
       """This Remote Metadata Adapter sample class shows a minimal custom
       implementation of the notify_user_message method.
       """
   
       def notify_user_message(self, user, session_id, message):
           """Invoked to forward a message received by a User"""
           print("Message {} arrived for user {} in the session {}"
                 .format(user, session_id, message))

4. Run the adapters, by creating, configuring and starting the server class instances:

   if __name__ == "__main__":
       # The host of the Lightstreamer server, to be changed as required.
       LS_SERVER_HOST = 'localhost'
   
       # Creates a new MetadataProviderServer instance, passing a new
       # MyMetadataAdpater object and the remote address.
       metadata_provider_server = MetadataProviderServer(MyMetadataAdapter(),
                                                         (LS_SERVER_HOST, 8003))
   
       # Starts the server instance.
       metadata_provider_server.start()
   
       # Creates a new DataProviderServer instance, passing a new MyDataAdpater
       # object and the remote address
       data_provider_sever = DataProviderServer(MyDataAdapter(),
                                                (LS_SERVER_HOST, 8001))
       # Starts the server instance.
       data_provider_sever.start()

5. Ensure that the main thread stays alive. This is needed, since Python 3.9, to allow the SDK library to take advantage of the system's ThreadPoolExecutor class. Here we show a simple way to do so:

   from threading import Event
   
   .....
   
   shutdown_event = Event()
   shutdown_event.wait()

Run

From the command line, execute:

$ python adapters.py

Connect a Client

var lsClient = new LightstreamerClient(LS_SERVER_HOST, "PROXY_PYTHON");
lsClient.connect();
// To be completed with other client side activities, like registration of subscriptions and handling of
// real time updates.
// ...

where LS_SERVER_HOST is the host of the Lightstreamer Server, and "PROXY_PYTHON" is the Adapter Set ID as specified in the adapters.xml file.

API Reference

API Reference is available at https://lightstreamer.com/api/ls-python-adapter/1.3.1/.

You can generate it by executing the following command from the doc folder:

$ make html

The generated documentation will be available under the doc\_build\html folder.

See Also

• Adapter Remoting Infrastructure Network Protocol Specification
• Lightstreamer Chat Demo adapter for Python

Lightstreamer Compatibility Notes

Compatible with Adapter Remoting Infrastructure since Server version 7.4. - For a version of this library compatible with Adapter Remoting Infrastructure for Server version 7,3, please refer to this tag. - For a version of this library compatible with Adapter Remoting Infrastructure for Server version 6.0 (corresponding to Adapter Remoting Infrastructure 1.7), please refer to this older tag.