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POPython: appending/merging multiple csv files respecting headers and write to csv
 

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  1. POPython: appending/merging multiple csv files respecting headers and write to csv
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    <p>[Using Python3] I'm very new to (Python) programming but nonetheless am writing a script that scans a folder for certain csv files, then I want to read them all and append them and write them into another csv file.</p> <p>In between it is required that data is returned only where the values in a certain columns are matched to a set criteria.</p> <p>All csv files have the same columns, and would look somewhere like this:</p> <pre><code>header1 header2 header3 header4 ... string float string float ... string float string float ... string float string float ... string float string float ... ... ... ... ... ... </code></pre> <p>The code I'm working with right now is the following (below), however it just keeps on overwriting the data from the previous file. That does make sense to me, I just cannot figure out how to get it working though.</p> <p>Code:</p> <pre><code>import csv import datetime import sys import glob import itertools from collections import defaultdict # Raw data files have the format like '2013-06-04'. To be able to use this script during the whole of 2013, the glob is set to search for the pattern '2013-*.csv' files = [f for f in glob.glob('2013-*.csv')] # Output file looks like '20130620-filtered.csv' outfile = '{:%Y%m%d}-filtered.csv'.format(datetime.datetime.now()) # List of 'Header4' values to be filtered for writing output header4 = ['string1', 'string2', 'string3', 'string4'] for f in files: with open(f, 'r') as f_in: dict_reader = csv.DictReader(f_in) with open(outfile, 'w') as f_out: dict_writer = csv.DictWriter(f_out, lineterminator='\n', fieldnames=dict_reader.fieldnames) dict_writer.writeheader() for row in dict_reader: if row['Campaign'] in campaign_names: dict_writer.writerow(row) </code></pre> <p>I also tried something like <code>readers = list(itertools.chain(*map(lambda f: csv.DictReader(open(f)), files)))</code>, and trying to iterate over the readers however then I cannot figure out how to work with the headers. (I get the error that itertools.chain() does not have the fieldnames attribute).</p> <p>Any help is very much appreciated!</p>
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