The simplest and probably most efficient way would be to make the script
add the data to two files: 1) the accumulating file you have now and 2) a
single line file which is the one which you read into pond.py
or you could do something like (not tested):
seek to end of file, go back one max line length, start to read lines, get
one line back from end
myfile.seek(-max_line_length, os.SEEK_END)
line = myfile.readlines()[-1]
in pond.py
On Saturday, 7 April 2018 23:51:39 UTC+3, vigilancewx wrote:
> Hello
>
>
> I have a current cost electricity meter connect to a linux computer via a
> usb cable
>
> On the linux computer is a script that every 20seconds loggs the watt and
> temp readings from the current cost meter to a txt file and RRD file
>
>
> I can generate the RRD graphs into the weewx public_html directory and
> display them accrodingly
>
>
> I know that weewx is predominatly for displaying weather data but I would
> like weewx to handle the watt data, so I have tried to save the readings
> into the weewx.sdb
>
>
> I found this version of pond.py from the weewx user groups and it works
> with no errors
>
>
>
> Following advice given in the weewx help files I can now display the data
> in the various html files display graphs etc
>
>
> I have one problem, pond.py takes the readings from the first line in the
> txt file (readings.txt)
>
>
> how do I modify pond.py to take its readings from the last line of the txt
> file, because file the last line of my txt file holds the latest data
>
>
> thank you for any help
>
>
> import syslog
>
> import weewx
>
> from weewx.wxengine import StdService
>
>
> class PondService(StdService):
>
> def __init__(self, engine, config_dict):
>
> super(PondService, self).__init__(engine, config_dict)
>
> d = config_dict.get('PondService', {})
>
> self.filename = d.get('filename', '/var/www/html/data/reading.txt')
>
> syslog.syslog(syslog.LOG_INFO, "pond: using %s" % self.filename)
>
> self.bind(weewx.NEW_ARCHIVE_RECORD, self.read_file)
>
>
> def read_file(self, event):
>
> try:
>
> with open(self.filename) as f:
>
> #value = f.read()
>
> line = f.readline()
>
> value = line.split(',')
>
> syslog.syslog(syslog.LOG_DEBUG, "pond: found value of %s" % value)
>
> event.record['ccwatt'] = float(value[0])
>
> event.record['cctemp'] = float(value[1])
>
> except Exception, e:
>
> syslog.syslog(syslog.LOG_ERR, "pond: cannot read value: %s" % e)
>
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