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I am currently in some truble regarding python and reading files. I have to open a file in a while loop and do some stuff with the values of the file. The results are written into a new file. This new file is then read in the next run of the while loop. But in this second run I get no values out of this file... Here is a code snippet, that hopefully clarifies what I mean.

Thanks in advance!!!

while convergence == 0:
    run += 1
    prevrun = run-1

    if os.path.isfile("./Output/temp/EmissionMat%d.txt" %prevrun) == True:
        matfile = open("./Output/temp/EmissionMat%d.txt" %prevrun, "r") 
        EmissionMat = Aux_Functions.EmissionMat(matfile)
        matfile.close()
    else:
        matfile = open("./Input/EmissionMat.txt", "r") 
        EmissionMat = Aux_Functions.EmissionMat(matfile)
        matfile.close()

    # now some valid operations, which produce a matrix

    emissionmat_file = open("./output/temp/EmissionMat%d.txt" %run, "w")
    emissionmat_file.flush()
    emissionmat_file.write(str(matrix))

    emissionmat_file.close()

!!!!!!!!!!!

Solved it!

matfile.seek(0)

This resets the pointer to the begining of the file and allows me to read the file in the next run correctly. Thanks everyone!!!

!!!!!!!!!!!

share|improve this question
why do you emissionmat_file.flush() before writing, and what is the content of matrix – njzk2 35 mins ago
What OS are you using? – interjay 32 mins ago
@interjay I am using Win7. – swot 27 mins ago
@njzk2 I do emissionmat_file.flush() to get the content to my file otherwise i get no values in my file. The content of matrix is a numpy array with 40*40 values. But do not mind the write stuff. The resulting file looked as it is desired. I just simplified it here. – swot 26 mins ago
do you have a typo in your code? "./Output" and "./output" is not the same... pro tip: use a constant/variable for this... – Daren Thomas 24 mins ago
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2 Answers

up vote 0 down vote

I can see nothing wrong with your code. The following concrete example worked on my Linux machine:

import os

run = 0
while run < 10:
    run += 1
    prevrun = run-1

    if os.path.isfile("output%d.txt" %prevrun):
        matfile = open("output%d.txt" %prevrun, "r")
        data = matfile.readlines()
        matfile.close()
    else:
        matfile = open("input.txt", "r")
        data = matfile.readlines()
        matfile.close()

    data = [ s[:-1] + "!\n" for s in data ]

    emissionmat_file = open("output%d.txt" %run, "w")
    emissionmat_file.writelines(data)
    emissionmat_file.close()

It adds an exclamation mark to each line in the file input.txt.

share|improve this answer
As you can see in the question post I solved the problem. I will put it in a "real" answer as soon as the system allows me to do this. Thanks for your help. – swot 2 mins ago
up vote 0 down vote

Why to write to a file and then read it ? Moreover you use flush, so you are doing potentially long io. I would do

with open(originalpath) as f:
    mat = f.read()
while condition :
    run += 1
    write_mat_run(mat, run)
    mat = func(mat)

write_mat_run may be done in another thread. You should check io exceptions.

BTW this will probably solve your bug, or at least make it clear.

share|improve this answer
This is part of an expectation maximization algorithm so i need the values from the previous run for the current run. – swot 7 mins ago
I solved it (see question post) I will post it as a "real" answer if the system allows me to. But thanks for your help! – swot 3 mins ago

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