Double call of update_sensor() when getting altitude

[JimMadge]

Hi,

I noticed that update_sensor() appears to be called twice in a row when calling get_altitude. First self.update_sensor() is called followed by self.get_pressure(),

bme280-python/library/bme280/__init__.py

Lines 275 to 279 in 97c80ce

	def get_altitude(self, qnh=1013.25):
	self.update_sensor()
	pressure = self.get_pressure()
	altitude = 44330.0 * (1.0 - pow(pressure / qnh, (1.0 / 5.255)))
	return altitude

However, the first line of get_pressure is also self.update_sensor(),

bme280-python/library/bme280/__init__.py

Lines 267 to 269 in 97c80ce

	def get_pressure(self):
	self.update_sensor()
	return self.pressure

So, if we unrolled this we would get something like

self.update_sensor()
self.update_sensor()
pressure = self.pressure

I'm happy to open a PR changing this if it isn't intended.

[Gadgetoid]

It's a side-effect of the fact it makes sense for all the readings to be processed at once, coupled with the fact I prefer methods over attributes for getting values... and you kind of expect a method to do something and fetch the data.

There are ways this could be mitigated, but it's one of those cases where running update_sensor() twice probably hurts less than contriving some method to prevent it.

With the benefit of hindsight, I'd probably rewrite the whole library API 😬 but since we can't really do that, I'm open to suggestions!

[JimMadge]

It's a side-effect of the fact it makes sense for all the readings to be processed at once

On that point, it did occur to me that adding a get_readings method which returns a tuple (temperature, pressure, humidity) would be a nice addition for those who want to get all of the values, particularly in forced mode. I could do that if you'd like.

coupled with the fact I prefer methods over attributes for getting values...

This is precisely the kind of thing that makes me spend a day agonising over how I should do something rather than actually doing it 😆 . Python's flexibility can be a blessing and a curse.

I think it would be safe to remove self.update_sensor() from get_altitude as it will always be called anyway on the first line of get_pressure (and get_pressure requires that line to function correctly).