This question is more related to python programming than using weewx, but I
cant find a solution - so I hope that Tom and the other gurus can point me
in the right direction.
I am writing a function to capture power consumption from the utility
meter. As part of that I am storing the cumulative energy reading for each
archive period in the archive.
To get the incremental energy reading between archive periods I read the
last archive record of the cumulative energy with the "latest" function in
weewx.tags. Reading and printing the latest archive record of cumulative
energy works fine - here is a snippet of the code to do that (thanks to
Tom's answers to previous threads)
# Create a RecordBinder, bound to the database and timestamp
rb = weewx.tags.RecordBinder(db_lookup, timestamp)
print "The last cumulative electrical energy record =",
rb.latest().cumEnergy
When I try to subtract the value for rb.latest().cumEnergy from the current
cumulative energy reading just obtained from the meter, I get a type error.
Then I added the following code to try and figure out what the out type of
rb.latest().cumEnergy
is
last_cum_energy = rb.latest().cumEnergy
print type(last_cum_energy)
This does not help because the output of the last print command is
<class 'weewx.units.ValueHelper'>
I tried doing a float modification, but that does not work.
Any help to turn the output of the function into something I can do
arithmetic with will be appreciated.
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