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  1. PO
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    <p>You cannot add columns to an existing CSV file; you'll have to rewrite the whole file, I'm afraid.</p> <p>You can use the following context manager to make replacing a file a little easier:</p> <pre><code>from contextlib import contextmanager import io import os @contextmanager def inplace(filename, mode='r', buffering=-1, encoding=None, errors=None, newline=None, backup_extension=None): """Allow for a file to be replaced with new content. yields a tuple of (readable, writable) file objects, where writable replaces readable. If an exception occurs, the old file is restored, removing the written data. mode should *not* use 'w', 'a' or '+'; only read-only-modes are supported. """ # move existing file to backup, create new file with same permissions # borrowed extensively from the fileinput module if set(mode) &amp; set('wa+'): raise ValueError('Only read-only file modes can be used') backupfilename = filename + (backup_extension or os.extsep + 'bak') try: os.unlink(backupfilename) except os.error: pass os.rename(filename, backupfilename) readable = io.open(backupfilename, mode, buffering=buffering, encoding=encoding, errors=errors, newline=newline) try: perm = os.fstat(readable.fileno()).st_mode except OSError: writable = open(filename, 'w' + mode.replace('r', ''), buffering=buffering, encoding=encoding, errors=errors, newline=newline) else: os_mode = os.O_CREAT | os.O_WRONLY | os.O_TRUNC if hasattr(os, 'O_BINARY'): os_mode |= os.O_BINARY fd = os.open(filename, os_mode, perm) writable = io.open(fd, "w" + mode.replace('r', ''), buffering=buffering, encoding=encoding, errors=errors, newline=newline) try: if hasattr(os, 'chmod'): os.chmod(filename, perm) except OSError: pass try: yield readable, writable except Exception: # move backup back try: os.unlink(filename) except os.error: pass os.rename(backupfilename, filename) raise finally: readable.close() writable.close() try: os.unlink(backupfilename) except os.error: pass </code></pre> <p>Use this with the <code>csv</code> module to add columns:</p> <pre><code>with inplace(csvfilename, 'rb') as (infh, outfh): reader = csv.reader(infh) writer = csv.writer(outfh) for row in reader: row += ['new', 'column'] writer.writerow(row) </code></pre>
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    1. POAdd columns to CSV while writing the CSV
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    1. USMartijn Pieters
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    1. POAdd columns to CSV while writing the CSV
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    1. COThank you for input, your solution is very elegant, but I am an engineer, so I will use a horrible merge.
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      1. USfabio.geraci
    2. COThe contextmanager is posted as a blog post, expanding support a little: http://www.zopatista.com/python/2013/11/26/inplace-file-rewriting/
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