save data from a command to a csv file in python

Question

I want to save the result of a command in a csv file. I have this code for the moment :

import sys
import os
import time
import datetime
import subprocess
import csv

with open("compteur_data.csv","a") as csvfile:
            date = datetime.datetime.today()
            wtr=csv.writer(csvfile)
            wtr.writerow(['Date/Heure','DATA']) #pillar title
            while True:
                ts = time.time()
                st = datetime.datetime.fromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
                print '..............................', st
                sys.stdout.flush()
                cmd = 'sdm120c -a 1 -b 2400 -P N -S 2 -j 20 -z 1 /dev/ttyUSB0'
                (c_stdin,c_stdout,c_stderr)=os.popen3(cmd,'r')
                out=c_stdout.read()
                print out
                c_stdin.close()
                c_stdout.close()
                c_stderr.close()

                wtr.writerow([date,out])
                time.sleep(5)

My purpose is to collect the data from a sdm120c , then, save the data in a csv file. On my python shell i can see all the data i want save every 5 seconds but when i open the target csv file nothing is write in .. Maybe some one can ask me where is my mistake ? please .

are you getting ValueError: popen3() arg 2 must be 't' or 'b' like me? — Ulf Gjerdingen
– Ulf Gjerdingen, Commented Jun 29, 2016 at 14:28
I have no error at the compilation the 'r' was accepted.I am on python 2.7.9 , maybe it's why you have this .. and all the data of my command was print. — Thibzy
– Thibzy, Commented Jun 29, 2016 at 14:39

Luke Taylor · Accepted Answer · 2016-06-29 14:40:30Z

2

Add a call to flush the buffered contents to the file. This is achieved by using the call: csvfile.flush()

with open("compteur_data.csv","a") as csvfile:
    date = datetime.datetime.today()
    wtr=csv.writer(csvfile)
    wtr.writerow(['Date/Heure','DATA']) #pillar title
    while True:
        ts = time.time()
        st = datetime.datetime.fromtimestamp(ts).strftime('%Y-%m-%d %H:%M:%S')
        print '..............................', st
        sys.stdout.flush()
        cmd = 'sdm120c -a 1 -b 2400 -P N -S 2 -j 20 -z 1 /dev/ttyUSB0'
        (c_stdin,c_stdout,c_stderr)=os.popen3(cmd,'r')
        out=c_stdout.read()
        print out
        c_stdin.close()
        c_stdout.close()
        c_stderr.close()

        wtr.writerow([date,out])

        #New call to flush added below
        csvfile.flush()

        time.sleep(5)

edited Jun 29, 2016 at 14:40

Luke Taylor

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answered Jun 29, 2016 at 14:30

jhrf

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1 Comment

Thibzy Over a year ago

Thanks for your help! really ! now I can see the value in my csv file !!

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