How to write last 50 lines from one file to another Python

Question

I am creating an email response to an overnight build, I want to get the last 50 lines from the results file and place it into a summary file. The code that I have done is below, can anyone help?

def email_success():

    fp = open(results_file, 'r')

    sum_file = (fp.readlines()[-50:])
    fp.close()

    myfile = open(result_summary,'w')

    myfile.write(sum_file)
    myfile.close()

I have got the error message below when trying this code:

Traceback (most recent call last):
  File "email_success.py", line 76, in <module>
    if __name__ == '__main__': myObject = email_success()
  File "email_success.py", line 45, in email_success
    myfile = open(result_summary,'w')
TypeError: coercing to Unicode: need string or buffer, tuple found

Thanks

The results summary is a variable that stores an address.

result_summary = (t, 'results_summary.txt')

Sorry made a stupid mistake, I forgot to add os.path.join

result_summary = os.path.join(t, 'results_summary.txt')

Thanks for the help

@alok It is a directory address, I forgot to add the os.join to make it one string. This is what was causing the error

replace `write` with `writelines`, and get rid of `()` surrounding the `readlines()` call. — Alok Singhal, Jan 06 '10 at 10:07
@chris: What do you think `open((t, 'results_summary.txt'), 'w')` means? — Alok Singhal, Jan 06 '10 at 10:19
If you're using linux/unix you could use `tail -n 50 input.txt > output.txt`. — Georg Schölly, Jan 06 '10 at 10:42
Duplicate: http://stackoverflow.com/questions/136168/get-last-n-lines-of-a-file-with-python-similar-to-tail. Likely homework. — S.Lott, Jan 06 '10 at 11:03

YOU · Answer 1 · 2010-01-06T10:13:38.687

5

TypeError: coercing to Unicode: need string or buffer, tuple found

Error says its expect string or buffer but you are passing tuple, so just join it with "" to make it to string

So, Try

sum_file = "".join(fp.readlines()[-50:])

UPDATE: because OP updated the question

if result_summary = (t, 'results_summary.txt')

Try

myfile = open(result_summary[1],'w')

edited Jan 06 '10 at 10:13

answered Jan 06 '10 at 10:06

YOU

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score 2 · Answer 2 · answered Jan 06 '10 at 10:11

2

It's open() raising the exception though... how did you define result_summary?

answered Jan 06 '10 at 10:11

Andrew McGregor

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score 2 · Accepted Answer · answered Jan 06 '10 at 10:11

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result_summary is a tuple, it needs to be either a str or buffer. Your explanation has nothing to do with the error you posted.

answered Jan 06 '10 at 10:11

SilentGhost

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score 1 · Answer 4 · answered Jan 06 '10 at 10:18

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result_summary = (t, 'results_summary.txt')

and

 myfile = open(result_summary,'w')

means

 myfile = open((t, 'results_summary.txt'),'w')

which obviously won't work, try:

 myfile = open(result_summary[1],'w')

instead

answered Jan 06 '10 at 10:18

Kimvais

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score 0 · Answer 5 · answered Jan 06 '10 at 10:10

0

fp.readlines() method returns a list of lines. Therefore you can't apply [-50:] operator.

answered Jan 06 '10 at 10:10

Upul Bandara

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That's wrong, you can definitely do `a[-50:]` when `a` is of type `list`. – Alok Singhal Jan 06 '10 at 10:28

How to write last 50 lines from one file to another Python

5 Answers5