Assuming the number of files is unknown, and that all the files are properly formatted as csv have the same number of lines:
files = ['csv1', 'csv2', 'csv3']
fs = map(open, files)
done = False
while not done:
chunks = []
for f in fs:
try:
l = next(f).strip()
chunks.append(l)
except StopIteration:
done = True
break
if not done:
print ','.join(chunks)
for f in fs:
f.close()
There seems to be no easy way of using context managers with a variable list of files easily, at least in Python 2 (see a comment in the accepted answer here), so manual closing of files will be required as above.