When $GPGGA is not the first sentence in a chunk, don't ignore the whole chunk but skip sentences up to the occurence of $GPGGA.
Tidied up coding style to PEP8 conventions on the way.
Finally (and most important), do interpret negative longitudes (indicated by 'W') and negative latitudes (indicated by 'S').
Started working recently on the same issues. Will temporarily merge into dev branch for merging with my changes and later on make a release on master. Thanks a lot!
When $GPGGA is not the first sentence in a chunk, don't ignore the whole chunk but skip sentences up to the occurence of $GPGGA. Tidied up coding style to PEP8 conventions on the way. Finally (and most important), do interpret negative longitudes (indicated by 'W') and negative latitudes (indicated by 'S').