| I guess this is as good a time as any to ask if None is the way Weewx represents a nonexistent element of data for the result of a query to any of its API functions. For example, if I want the barometric pressure at 9am, and no pressure was recorded around that time, is it None that would be returned?
Is there ever a case where (like in some other Python packages) NaN is used?
Sent from my iPhone Admittedly more elegant, thanks! Like I said, I'm still getting into Python, so I wasn't aware one could apply get() here. I usually have a fair understanding of what code does and can generate pseudocode of what I want, but implementing that in proper Python code is what I struggle with.
On Saturday, May 4, 2024 at 2:59:47 PM UTC-5 Tom Keffer wrote:
Or, combining into one step...
if event.record.get('rain') is not None: do something
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
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}
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:
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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