python - writing into .csv-file inside of "while"-loop -


by using 

result = open("data/"+ name + "_" + timestamp + ".csv", "w") result.write("time; data1; data2; data3 \n")`

i open file , fill column identifiers.

using 

while true:     timestamp = time.strftime("%h:%m:%s", time.localtime())     data1,data2,data3 = device.fetchdata()      result.write(timestamp +";"+ str(data1) +";"+ str(data1) +";"+ str(data3) +"\n")     time.sleep(seconds)

the .csv-file should filled measuring data. problem is, if check file after exiting script, it's completely empty, not column identifiers present. however, if use for-loop, works should.

very strange understanding.

i assume want leave program running indefinitely collect data kind of sensor, , suspect issue default buffering open() call.

firstly, should using "with" block @spirine suggests, in case slight modification in order:

with open("data/"+ name + "_" + timestamp + ".csv", "w", 1) result:

the , 1 @ end indicates line buffering, meaning python write file disk @ end of each line. also, consider using str.format() make bit more polished:

log_line_template = "{ts:%h:%m:%s};{d1};{d2};{d3}\n" filename = "data/{n}_{ts:%h_%m_%s}.csv".format(n=name, ts=datetime.now())  open(filename, "w", 1) result:     result.write("time; data1; data2; data3 \n")`      while true:         data1,data2,data3 = device.fetchdata()         result.write(log_line_template.format(             ts=datetime.now(), data1, data2, data3         ))         time.sleep(seconds)

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