In Python, how to write strings in a file in a loop and before the loop stops, I can get the results runtimely?

Question

In python, I need to record some results in a file. The results are generated by a function in a loop. The following code shows an example:

with open('result_file', 'w') as file:     
    for i in xrange(10000):
        result = somethingTakesTime()
        file.write(str(result), '\n')

Function somethingTakesTime() is time costly. I would like to check the result_file even the program is still working. However, with the current Python 2.7, I only can get the result after the for loop finish. Is there any method that I can see the result (in result_file) even the code is still working?

Are you interested in viewing the file in a text editor or having your script check previous results while the next one is being calculated? — skrrgwasme, Oct 23 '15 at 19:36
You can also set the buffer size to 0 bytes as described in [this SO answer](http://stackoverflow.com/a/3168436/2615940) so the buffering never happens in the first place. — skrrgwasme, Oct 23 '15 at 19:39
@ChadS. You should put that in an answer so it can be accepted. — skrrgwasme, Oct 23 '15 at 19:42

score 2 · Accepted Answer · answered Oct 23 '15 at 19:47

When programs write data to files, they usually keep the data in an internal buffer to prevent frequent disk writes (which can slow things down). But if the generation of the data is slower than the disk write would otherwise be, it can sometimes be useful to tell the program that you'd like to flush the data immediately to the file. To do this you'd use the .flush method of the file object.

E.g.

with open('result_file', 'w') as file:     
    for i in xrange(10000):
        result = somethingTakesTime()
        file.write(str(result), '\n')
        file.flush()

In Python, how to write strings in a file in a loop and before the loop stops, I can get the results runtimely?

1 Answers1