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    <p>The problem with your code is that it keeps opening the same country output file each time it writes an entry into it, thereby overwriting whatever might have already been there.</p> <p>A simple way to avoid that is to open all the output files at once for writing and store them in a dictionary keyed by the country code. Likewise, you can have another that associates each country code to a<code>csv.writer</code>object for that country's output file.</p> <p><strong>Update:</strong> While I agree that Burhan's approach is probably superior, I feel that you have the idea that my earlier answer was excessively long due to all the comments it had -- so here's another version of essentially the same logic but with minimal comments to allow you better discern its reasonably-short true length (even with the contextmanager).</p> <pre><code>import csv from contextlib import contextmanager @contextmanager # to manage simultaneous opening and closing of output files def open_country_csv_files(countries): csv_files = {country: open('output-'+country+'.csv', 'w') for country in countries} yield csv_files for f in csv_files.values(): f.close() with open('email.tsv', 'r') as f: email_dict = {row[0]: row[1] for row in csv.reader(f, delimiter='\t') if row} countries = set(email_dict.values()) with open_country_csv_files(countries) as csv_files: csv_writers = {country: csv.writer(csv_files[country], lineterminator='\r\n') for country in countries} for email_addr,country in email_dict.items(): csv_writers[country].writerow([email_addr]) </code></pre>
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    1. POWrite key to separate csv based on value in dictionary
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    1. USmartineau
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    1. COThanks Martineau! Your solution did exactly what I had intended!
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    2. COMatthijs: If you think my answer is worthy, please consider also up-voting it (if you have sufficient rep yourself). Thanks.
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    3. COHi Martineau, unfortunately I don't have enough reputation yet. I would have done so otherwise of course.
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