Python: copy line, conditional criteria

Question

I have been searching for following Python solution to copy selectively lines from 1 txt file to another. I can copy the whole file, but with only a few lines I get an error.

My code:

    f = open(from_file, "r")
    g = open(to_file, "w")
    #copy = open(to_file, "w") # this instruction copies whole file
    rowcond2 = 'xxxx' # look for this string sequence in every line

    for line in f:
        if rowcond2 in f:
            copy.write(line,"w") in g # write every corresponding line to  destination

    f.close()
    # copy.close() # code receive error to close destination
    g.close()

So without the rowcond2, I can copy the whole file. Yet with the condition nothing is written to destination file.

Thank you for your help.

What is exactly rowcond2 is supposed to do? Or what kind of condition you're willing to have? — Gabor, Jan 15 '16 at 18:38
'rowcond2' stands for a string sequence in a line of txt file (e.g. 'xxxx'). — user1739581, Jan 15 '16 at 19:46

score 0 · Answer 1 · answered Jan 15 '16 at 18:43

0

Why not to put your condition inside the for loop?

for line in f:
    if condition:
        copy.write(line)

answered Jan 15 '16 at 18:43

Gabor

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This helps! My coding is still confused between the 2 files. With your suggestion, I have corrected code (see my 1st entry). – user1739581 Jan 15 '16 at 19:35

score 0 · Answer 2 · edited May 23 '17 at 12:31

0

I have been able to solve this case searching on SO:

Using python to write specific lines from one file to another file

@Lukas Graf: thank you for your detailed step wise explanation.

edited May 23 '17 at 12:31

Community

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answered Jan 16 '16 at 17:53

user1739581

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Python: copy line, conditional criteria

2 Answers2