python: defeat or reduce input buffer when reading from a device

Question

(python 2.7.9 on raspbian on raspberry hardware) Reading GPS data from a serial port, I find no way to defeat input buffering. This makes my data come in big blurbs with far too much time in between. I searched this site, and others, and applied "buffering" in various forms (buffering=0, buffering=-1, buffering=5, ... ) on the open statement, all to no avail.

INPORT='/dev/ttyAMA0'
with open(INPORT,'rb',buffering=-1) as infile:
 for INLIN in INFILE:
  INFIELD=INLIN.split(",")
   if INFIELD[0][0:1] == "$":
    print datetime.datetime.now(),INFIELD[0]

sample of output:

2016-04-17 11:59:20.469383 $GNGSA
2016-04-17 11:59:20.471004 $GPGSV
2016-04-17 11:59:20.472660 $GPGSV
2016-04-17 11:59:20.475128 $GPGSV
2016-04-17 11:59:20.475743 $GPGSV
2016-04-17 11:59:20.477228 $GLGSV
2016-04-17 11:59:20.478902 $GLGSV
2016-04-17 11:59:20.480494 $GLGSV
2016-04-17 11:59:20.481994 $GNGLL
2016-04-17 11:59:20.483569 $GNRMC
2016-04-17 11:59:20.484283 $GNVTG
2016-04-17 11:59:33.681551 $GNGGA
2016-04-17 11:59:33.682010 $GNGSA
2016-04-17 11:59:33.682357 $GNGSA
2016-04-17 11:59:33.682693 $GPGSV
2016-04-17 11:59:33.683025 $GPGSV
2016-04-17 11:59:33.683359 $GPGSV
2016-04-17 11:59:33.683680 $GPGSV
2016-04-17 11:59:33.684017 $GLGSV
2016-04-17 11:59:33.684467 $GLGSV

Sorry, Padraic, no good: for INLIN iter(infile.readline,""): ^ SyntaxError: invalid syntax — Karel Adams
– Karel Adams, Commented Apr 17, 2016 at 12:18
Sorry was missing the in for INLIN in iter(infile.readline,"") — Padraic Cunningham
– Padraic Cunningham, Commented Apr 17, 2016 at 12:42
All clear, Padraig, I must admit I could have found that out by myself if I were less lazy. Many thanks! — Karel Adams
– Karel Adams, Commented Apr 17, 2016 at 13:04

Karel Adams · Accepted Answer · 2016-04-17 13:02:06Z

1

with open(INPORT,'rb',buffering=-1) as infile:
 for INLIN in iter(infile.readline,""):
  INFIELD=INLIN.split(",")
  if INFIELD[0] == "$GPRMC" or INFIELD[0] == "$GNRMC":
   print datetime.datetime.now(),INLIN

(as suggested) does the trick perfectly - many thanks to Padraig!

2016-04-17 12:59:23.119878 $GNRMC,125923.00,A,5058.48999,N,00437.42029,E,0.050,,170416,,,D*65
2016-04-17 12:59:24.119874 $GNRMC,125924.00,A,5058.48998,N,00437.42032,E,0.066,,170416,,,D*6C
2016-04-17 12:59:25.119593 $GNRMC,125925.00,A,5058.48999,N,00437.42034,E,0.070,,170416,,,D*6D
2016-04-17 12:59:26.121776 $GNRMC,125926.00,A,5058.49001,N,00437.42033,E,0.082,,170416,,,D*6D
2016-04-17 12:59:27.119076 $GNRMC,125927.00,A,5058.49002,N,00437.42033,E,0.025,,170416,,,D*62
2016-04-17 12:59:28.119765 $GNRMC,125928.00,A,5058.49003,N,00437.42035,E,0.113,,170416,,,D*6E

answered Apr 17, 2016 at 13:02

Karel Adams

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