Iterate through a Talker Sentence

[montge]

I'm trying to figure out the best way to parse through the fields in a talker.

type(pynmea2.parse("$GPGSV,...")) produces <class 'pynmea2.types.talker.GSV'>

A bit of exploring didn't seem to come up with a good solution, without having to follow how the test code is setup where you have to know before you do.

>>> msg = pynmea2.parse("$GPGSV,...")
>>> msg.__dict__.keys()
dict_keys(['talker', 'sentence_type', 'data'])
>>> variables = [i for i in dir(msg) if not callable(i)]
>>> variables
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattr__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'checksum', 'data', 'fields', 'identifier', 'name_to_idx', 'parse', 'proprietary_re', 'query_re', 'render', 'sentence_re', 'sentence_type', 'sentence_types', 'talker', 'talker_re']

I was trying to target something like the following.

import sys
import os
import time
import pynmea2

def read(filename):
    f = open(filename)
    reader = pynmea2.NMEAStreamReader(f)

    while 1:
        for msg in reader.next():
            decode_msg = pynmea2.parse(str(msg))
            print(msg)
            for key in decode_msg:
                value = decode_msg[key]
                print(key, " :: ", value)

def main():
    read(sys.argv[1])

main()

However I get the following response.

Traceback (most recent call last):
  File "convert.py", line 21, in <module>
    main()
  File "convert.py", line 19, in main
    read(sys.argv[1])
  File "convert.py", line 14, in read
    for key in msg:
TypeError: 'GSV' object is not iterable

I also tried a variant with

for talker, sentence_type, data in decode_msg.items():
                print(talker, " :: ", sentence_type , " :: ", data)

but got

Traceback (most recent call last):
  File "/anaconda3/lib/python3.7/site-packages/pynmea2/nmea.py", line 153, in __getattr__
    i = t.name_to_idx[name]
KeyError: 'items'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "convert.py", line 20, in <module>
    main()
  File "convert.py", line 18, in main
    read(sys.argv[1])
  File "convert.py", line 14, in read
    for talker, sentence_type, data in decode_msg.items():
  File "/anaconda3/lib/python3.7/site-packages/pynmea2/nmea.py", line 155, in __getattr__
    raise AttributeError(name)
AttributeError: items

suggestions welcome!

[Knio]

Hi,
This was an unanticipated usage, and I realize there is no nice, documented API for it. Thanks for pointing this out.

Here is one way to do this today:

msg = pynmea2.parse("$GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D")
fields = {k: getattr(msg, k) for k in msg.name_to_idx}
print(fields)

Output:

{'timestamp': datetime.time(18, 43, 53, 70000), 'lat': '1929.045', 'lat_dir': 'S', 'lon': '02410.506', 'lon_dir': 'E', 'gps_qual': 1, 'num_sats': '04', 'horizontal_dil': '2.6', 'altitude': 100.0, 'altitude_units': 'M', 'geo_sep': '-33.9', 'geo_sep_units': 'M', 'age_gps_data': '', 'ref_station_id': '0000'}

Note that not all NMEA messages map cleanly to key-value pairs, and some types will have extra data that will not appear in fields there. See nmea.py:180 (__repr__) as a further example.

I will leave this ticket open for myself to create a better public facing API for this usage.

[montge]

Thanks! Might suggest just adding it to the example code.

[xOneca]

There are fields like latitude, longitude, datetime, etc. (i.e. those on mixins) that are dynamic properties and don't show on name_to_idx. It would be nice to consider them, if possible, in that future new API...