pypck - Asynchronous LCN-PCK library written in Python

Overview

pypck is an open source library written in Python which allows the connection to the LCN (local control network) system. It uses the vendor protocol LCN-PCK. To get started an unused license of the coupling software LCN-PCHK and a hardware coupler is necessary.

pypck is used by the LCN integration of the Home Assistant project.

Example

"""Example for switching an output port of module 10 on and off."""
import asyncio

from pypck.connection import PchkConnectionManager
from pypck.lcn_addr import LcnAddr

async def main():
    """Connect to PCK host, get module object and switch output port on and off."""
    async with PchkConnectionManager(
        "192.168.2.41",
        4114,
        username="lcn",
        password="lcn",
        settings={"SK_NUM_TRIES": 0},
    ) as pck_client:
        module = pck_client.get_address_conn(LcnAddr(0, 10, False))

        await module.dim_output(0, 100, 0)
        await asyncio.sleep(1)
        await module.dim_output(0, 0, 0)

asyncio.run(main())

pypck REPL in ipython

pypck relies heavily on asyncio for talking to the LCN-PCHK software. This makes it unusable with the standard python interactive interpreter. Fortunately, ipython provides some support for asyncio in its interactive interpreter, see ipython autoawait.

Requirements

• ipython at least version 7.0 (autoawait support)
• pypck

Example session

Python 3.8.3 (default, Jun  9 2020, 17:39:39)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.19.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: from pypck.connection import PchkConnectionManager
   ...: from pypck.lcn_addr import LcnAddr
   ...: import asyncio

In [2]: connection = PchkConnectionManager(host='localhost', port=4114, username='lcn', password='lcn')

In [3]: await connection.async_connect()

In [4]: module = connection.get_address_conn(LcnAddr(seg_id=0, addr_id=10, is_group=False), request_serials=False)

In [5]: await module.request_serials()
Out[5]:
{'hardware_serial': 127977263668,
 'manu': 1,
 'software_serial': 1771023,
 'hardware_type': <HardwareType.UPU: 26>}

In [6]: await module.dim_output(0, 100, 0)
   ...: await asyncio.sleep(1)
   ...: await module.dim_output(0, 0, 0)
Out[6]: True

Caveats

ipython starts and stops the asyncio event loop for each toplevel command sequence. Also it only starts the loop if the toplevel commands includes async code (like await or a call to an async function). This can lead to unexpected behavior. For example, background tasks run only while ipython is executing toplevel commands that started the event loop. Functions that use the event loop only internally may fail, e.g. the following would fail:

In [4]: module = connection.get_address_conn(LcnAddr(seg_id=0, addr_id=10, is_group=False), request_serials=True)
---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-7-cd663974bde2> in <module>
----> 1 module = connection.get_address_conn(modaddr)

/pypck/connection.py in get_address_conn(self, addr, request_serials)
    457                 address_conn = ModuleConnection(self, addr)
    458                 if request_serials:
--> 459                     self.request_serials_task = asyncio.create_task(
    460                         address_conn.request_serials()
    461                     )

/usr/local/lib/python3.8/asyncio/tasks.py in create_task(coro, name)
    379     Return a Task object.
    380     """
--> 381     loop = events.get_running_loop()
    382     task = loop.create_task(coro)
    383     _set_task_name(task, name)

RuntimeError: no running event loop

See ipython autoawait internals for details.