pynmea2 Documentation

While NMEA sentences use the DDDMM.MMMM format, pynmea2 provides helper properties on NMEASentence objects to access coordinates as Python floats (Decimal Degrees).

Supported helpers:

• latitude / longitude: Returns decimal degrees as floats.
• latitude_minutes / longitude_minutes: Returns the minutes component.
• latitude_seconds / longitude_seconds: Returns the seconds component.

# Example of using coordinate helpers
msg = pynmea2.parse("$GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D")
print(msg.latitude)   # -19.4840833333
print(msg.longitude)  # 24.1751

Install the pynmea2 library using pip to begin parsing and generating NMEA 0183 sentences.

pip install pynmea2

When reading from a serial device, wrap the serial object in io.TextIOWrapper to handle line-based reading. Handle serial.SerialException for hardware errors and pynmea2.ParseError for malformed NMEA data.

import io
import pynmea2
import serial

ser = serial.Serial('/dev/ttyS1', 9600, timeout=5.0)
sio = io.TextIOWrapper(io.BufferedRWPair(ser, ser))

while 1:
    try:
        line = sio.readline()
        msg = pynmea2.parse(line)
        print(repr(msg))
    except serial.SerialException as e:
        print('Device error: {}'.format(e))
        break
    except pynmea2.ParseError as e:
        print('Parse error: {}'.format(e))
        continue

Iterate through a file line by line and pass each line to pynmea2.parse(). Wrap the call in a try/except block to handle pynmea2.ParseError for corrupt lines.

import pynmea2

file = open('examples/data.log', encoding='utf-8')

for line in file.readlines():
    try
        msg = pynmea2.parse(line)
        print(repr(msg))
    except pynmea2.ParseError as e:
        print('Parse error: {}'.format(e))
        continue

You can create a new NMEASentence object by calling the specific message class constructor (e.g., GGA) with the talker, message type, and a tuple of data fields. Use str(msg) to generate the formatted NMEA string.

import pynmea2
msg = pynmea2.GGA('GP', 'GGA', ('184353.07', '1929.045', 'S', '02410.506', 'E', '1', '04', '2.6', '100.00', 'M', '-33.9', 'M', '', '0000'))
print(str(msg))
# Output: $GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D

Use pynmea2.parse(data) to convert a NMEA 0183 sentence string into a NMEASentence object. The leading $ is optional and trailing whitespace is ignored.

By default, the function validates checksums. You can configure checksum behavior using the checksums argument.

import pynmea2
msg = pynmea2.parse("$GPGGA,184353.07,1929.045,S,02410.506,E,1,04,2.6,100.00,M,-33.9,M,,0000*6D")

The parse(data, checksums=...) function accepts three modes for handling checksums:

Note: Invalid checksums may also cause ParseError if the corruption prevents basic parsing.

# Example of using the checksums parameter
pynmea2.parse(data, checksums='required')