That did it, thanks, Frantisek!
I now check that if 'rain' is in event.record, then check if it is 
non-Null, and if those two conditions are true, 'rain' has a valid value 
and I can use it for arithmetic.

On Saturday, May 4, 2024 at 4:17:10 AM UTC-5 František Slimařík wrote:

> Hello,
>
> event.record is dictionary. If you do event.record["rain" ] = something 
> you add new key/value into dictionary (if doesn´t exists or overwrite 
> current value). In case packet doesn´t contain no value for rain, key/value 
> pair is not added. If you do something and you are not sure if key exist in 
> dictionary you should do:
>
> if "rain" in event.record:
>   do_something
>
>
> pá 3. 5. 2024 v 21:31 odesílatel Michael Frotscher <[email protected]> 
> napsal:
>
>> Even more unexpected, it seems I can write to those "undefined" 
>> variables, but trying to read them gives me a Key Error.
>> I have created a new field in the database called "raintotal", where I 
>> want to store the running total of the rainfall.
>> Trying to test this for being "None", gives:
>> CRITICAL __main__:     ****      if event.record['raintotal'] == None: 
>> CRITICAL __main__:     ****         ~~~~~~~~~~~~^^^^^^^^^^^^^ 
>> CRITICAL __main__:     ****  KeyError: 'raintotal' 
>> CRITICAL __main__:     ****  Exiting.
>>
>> But if I just write to it:
>>
>> event.record['raintotal'] = 12345
>>
>> That ends up in the database and doesn't throw an error.
>>
>> On Friday, May 3, 2024 at 2:06:22 PM UTC-5 Michael Frotscher wrote:
>>
>>> Same here, 'rain' is None unless it's raining, then it'll show data. I 
>>> haven't checked the raw packets, but in the archive table the numbers are 
>>> all multiples of my tipping bucket size, so that all makes sense.
>>> That's why I added the "check for Null/None" if-clause.
>>> But to be populated with data, 'rain' has to be defined. And weewx 
>>> crashes on that 
>>> if event.record['rain'] != None:
>>> clause. Do I need to check for a packet? like event.package?
>>> On Friday, May 3, 2024 at 12:29:38 PM UTC-5 František Slimařík wrote:
>>>
>>>> I believe "rain" is specific in this case. I was checking raw packets 
>>>> previously on my device and normally is rain "none" if it´s not raining ;) 
>>>> So it depends what your device is sending to weewx.
>>>>
>>>> raw packet: {'dateTime': 1642794129, 'usUnits': 1, 'rain_total': 0.0, 
>>>> 'barometer': 30.22, 'temperature_out': 28.7, 'dewpoint': 20.1, 
>>>> 'humidity_out': 69.0, 'wind_speed': 2.6, 'wind_gust': 2.6, 'wind_dir': 
>>>> 268.0, 'solar_radiation': 0.0, 'uv': 0.0, 'temperature_in': 70.1, 
>>>> 'humidity_in': 51.0, 'rain': None}
>>>>
>>>> pá 3. 5. 2024 v 15:37 odesílatel Michael Frotscher <[email protected]> 
>>>> napsal:
>>>>
>>>>> Hmm,
>>>>> ok, so it works for "pressure", which contains data in every archive 
>>>>> period and is not None.
>>>>> I've tried to substitute that with "rain", which is what I really 
>>>>> want. That is usually "Null/None" in the database, but gets the amount of 
>>>>> a 
>>>>> bucket tip added to it every time that happens.
>>>>> It is fed by MQTT, which publishes the bucket amount on every tip, and 
>>>>> that works. It even sums them up correctly if several bucket tips occur 
>>>>> in 
>>>>> an archive period.
>>>>>
>>>>> However, trying to retrieve that with "if event.record['rain'] != None
>>>>> :"
>>>>> I get a Key Error. Meaning the variable doesn't exist. Isn't every 
>>>>> weewx measurement in the dictionary?
>>>>> That happens with any measurement that's in the database but normally 
>>>>> "Null".
>>>>>
>>>>> I've tried to define it as Null/None in the init-part of the service 
>>>>> rain = None
>>>>>
>>>>> But still get the key error.
>>>>>
>>>>> Thanks!
>>>>> On Friday, May 3, 2024 at 7:30:12 AM UTC-5 Michael Frotscher wrote:
>>>>>
>>>>>> Thanks, guys!
>>>>>> I see my mistake now. It's not about strings/floats at all, but I 
>>>>>> wrongly assumed that all measurements that have values assigned to them 
>>>>>> (via LOOP or whatever) would already be defined as global variables.
>>>>>> That's obviously not the case, but assigning the last value to the 
>>>>>> variable via "event.record['pressure']" (as Frantisek pointed out) is 
>>>>>> necessary. I'm still not sure why that needs to be in single quotes, 
>>>>>> indicating a string and not a number.
>>>>>> I would have expected something like "event.record(pressure)".
>>>>>>
>>>>>> I have to admit that I have not found this in any examples out there, 
>>>>>> and not in the documentation for sure.
>>>>>>
>>>>>> But it's now doing what I want.
>>>>>>
>>>>>> On Friday, May 3, 2024 at 12:16:50 AM UTC-5 František Slimařík wrote:
>>>>>>
>>>>>>> I guess you want something like this:
>>>>>>>
>>>>>>> if event.record['pressure'] != None:
>>>>>>>   newpressure = (event.record['pressure'] * 10)
>>>>>>>   event.record['pb'] = newpressure
>>>>>>>
>>>>>>> Dne pátek 3. května 2024 v 3:38:01 UTC+2 uživatel Tom Keffer napsal:
>>>>>>>
>>>>>>>> On Thu, May 2, 2024 at 6:32 PM Michael Frotscher <[email protected]> 
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> Here's the full code of my service:
>>>>>>>>>      
>>>>>>>>>
>>>>>>>>    def new_archive_packet(self, event): 
>>>>>>>>>
>>>>>>>>>       if 'pressure' != None:
>>>>>>>>>         newpressure = ('pressure' * 10)
>>>>>>>>>         event.record['pb'] = newpressure
>>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> Strictly interpreted, you first ask whether the string "'pressure'" 
>>>>>>>> is equal to None. It's not, so we proceed to the next statement. Now 
>>>>>>>> you're 
>>>>>>>> trying to multiply a string ('pressure') by 10. Surprisingly, this 
>>>>>>>> will 
>>>>>>>> succeed, but likely does not give you the results you expect. The 
>>>>>>>> variable 
>>>>>>>> "newpressure" will actually be set to the string 
>>>>>>>> 'pressurepressurepressurepressurepressurepressurepressurepressurepressurepressure'.
>>>>>>>>  
>>>>>>>> That is, the string 'pressure' concatenated 10 times.
>>>>>>>>
>>>>>>>> You want a *variable* pressure, not the literal string 'pressure'. 
>>>>>>>> Where will it come from?
>>>>>>>>
>>>>>>>> I would suggest taking an online Python course if this is 
>>>>>>>> unfamiliar to you. 
>>>>>>>>
>>>>>>>> -tk
>>>>>>>>
>>>>>>>>
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>>>>>  
>>>>> <https://groups.google.com/d/msgid/weewx-development/8a2868e8-7f39-4038-acd5-c783572e2226n%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>> .
>>>>>
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> To view this discussion on the web visit 
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>>  
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>> .
>>
>

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