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I am writing to csv in python, and I was wondering why my output files are blank when the program completes running. First off, here is my code:

reader = csv.reader(open(location, 'rU'), delimiter = ',', quotechar = '"') writer = csv.writer(open('temp.csv', 'wb'), delimiter = ',', quotechar = '"') writer.writerow(["test", "test", "test", "test", "test", "test", "test"]) count = 0 for row in reader: if count != 0 and count < len(split): writer.writerow([row[0], row[1], row[2], row[3], row[4], row[5], split[count-1]]) count = count + 1

I know a few things about it:

  • When the program finishes, all that is written to 'temp.csv' is the "test" line. The rest of the document is empty.
  • If I force stop the program in the middle of running, there is in fact text being written to the file: it just gets wiped for some reason.
  • I've done some research, and lots of people have found that "closing" the csv file solves their problems, but that doesn't seem to work for me, unless I am missing something obvious!

Thanks in advance for your help!

Edit: here is some updated code I am working with:

infile = open(location, 'rU') outfile = open('temp.csv', 'wb') reader = csv.reader(infile, delimiter = ',', quotechar = '"') writer = csv.writer(outfile, delimiter = ',', quotechar = '"') split = email_text.split('NEW MESSAGE BEGINS HERE') count = 0 for row in reader: if count != 0 and count < len(split): writer.writerow([row[0], row[1], row[2], row[3], row[4], row[5], split[count-1]]) outfile.flush() count = count + 1 infile.close() outfile.close()
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    How would you close the file? You're not saving a file handle on which you could use the .close() method. Commented Jul 12, 2012 at 14:52
  • Aside: instead of manually incrementing count, you could use for count, row in enumerate(reader):. Commented Jul 12, 2012 at 14:54
  • @brian: I just had a crazy idea. Could you add a print count statement inside your loop and confirm that count is actually going up? Commented Jul 12, 2012 at 16:46

2 Answers 2

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You're not closing the file. While this may work fine if you're just reading a file, it's definitely not a good idea to do this when writing a file.

Use a context manager:

with open(location, 'rU') as infile, open('temp.csv', 'wb') as outfile: reader = csv.reader(infile, delimiter = ',', quotechar = '"') writer = csv.writer(outfile, delimiter = ',', quotechar = '"') ...

This ensures that the files will be closed when the with block is exited (even if it's because of an exception).

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7 Comments

Hi, I tried that, and i got an "Invalid syntax" error at the "with open(location, 'rU')" bit. Sorry, I'm new to python!
@brian: You must be using an old version of Python. with is available since Python 2.6 (and on Python 2.5 if you start your script with from __future__ import with_statement).
I'm using python 2.4.3, but I'm on a network, so I don't have privileges to install or update anything. Is there any way to read these in 2.4.3?
Whoa. How old is Python 2.4 again? Over 6 years? OK, well then no with statement for you. But you can still do infile = open(...) and outfile = open(...), then do reader = csv.reader(infile,...) etc., and finally call infile.close() and especially outfile.close().
Okay, I did this, and it still didn't leave me with anything in my outfile! I'm not sure what the problem is...
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Change the first two lines to save the opened file handles, and then include close invocations afterwards

reader_file = open(location, 'rU') writer_file = open('temp.csv', 'wb') reader = csv.reader(reader_file, delimiter = ',', quotechar = '"') writer = csv.writer(writer_file, delimiter = ',', quotechar = '"') # ... rest of code ... reader_file.close() writer_file.close()
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This didn't work for me, I am still left with an empty outfile!
There might be an issue with your if statement. Else, did you intend for the writer_file to be opened in binary mode?

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