ServiceBrowser handler argument overwrites zeroconf name

[nils-werner]

In the default pattern

import zeroconf

instance = zeroconf.Zeroconf()
browser = zeroconf.ServiceBrowser(
    instance,
    ['_osc._udp.local.'],
    handlers=[handler]
)

def handler(zeroconf, service_type, name, state_change):
    # I cannot use zeroconf.ServiceStateChange.Added here, because zeroconf is not the import but the argument
    pass

we have the problem that handler() is receiving a named argument zeroconf that overloads import zeroconf and that we cannot change. If I defined

def handler(zc, service_type, name, state_change):
    if state_change is zeroconf.ServiceStateChange.Added:
        print(name)

I would receive

TypeError: handler() got an unexpected keyword argument 'zeroconf'

To avoid it I would have to alias the import, which is a bit ugly:

import zeroconf as imported_zeroconf

def handler(zeroconf, service_type, name, state_change):
    if state_change is imported_zeroconf.ServiceStateChange.Added:
        print(name)

It would be nice if the arguments were to be passed in as positional arguments, or named differently, so that the names didn't clash.

[maxtruxa]

Quick workaround using a decorator:

from functools import wraps

def zeroconf_handler(handler):
    # `wrapper`'s argument names are important!
    @wraps(handler)
    def wrapper(zeroconf, service_type, name, state_change):
        handler(zeroconf, service_type, name, state_change)
    return wrapper

# ...

@zeroconf_handler
def handler(zc, type_, name, new_state):
    pass

browser = zeroconf.ServiceBrowser(
    instance,
    ['_osc._udp.local.'],
    handlers=[handler]
)

Just for completeness sake, this can easily be extended to support async callbacks, which prevents incorrect usage of ensure_future()/create_task() demonstrated in all the examples:

import asyncio
from functools import wraps

_zeroconf_pending_handler_tasks = set()
def async_zeroconf_handler(handler):
    # `wrapper`'s argument names are important!
    @wraps(handler)
    def wrapper(zeroconf, service_type, name, state_change):
        # Keep a reference to the task around until it's done, to prevent it from being garbage collected.
        task = asyncio.create_task(handler(zeroconf, service_type, name, state_change))
        _zeroconf_pending_handler_tasks.add(task)
        task.add_done_callback(_zeroconf_pending_handler_tasks.discard)
    return wrapper

# ...

@async_zeroconf_handler
async def handler(zc, type_, name, new_state):
    await asyncio.sleep(1)

browser = zeroconf.ServiceBrowser(
    instance,
    ['_osc._udp.local.'],
    handlers=[handler]
)