avoiding code duplication in Python code redux

Question

This is a followup to an earlier question. I got some good suggestions for that, so I thought I would try my luck again.

from itertools import takewhile

if K is None:
    illuminacond = lambda x: x.split(',')[0] != '[Controls]'
else:
    illuminacond = lambda x: x.split(',')[0] != '[Controls]' and i < K

af=open('a')
bf=open('b', 'w')
cf=open('c', 'w')

i = 0
if K is None:
    for line in takewhile(illuminacond, af):
        line_split=line.split(',')
        pid=line_split[1][0:3]
        out = line_split[1] + ',' + line_split[2] + ',' + line_split[3][1] + line_split[3][3] + ',' \
                                  + line_split[15] + ',' + line_split[9] + ',' + line_split[10]
        if pid!='cnv' and pid!='hCV' and pid!='cnv':
            i = i+1
            bf.write(out.strip('"')+'\n')
            cf.write(line)
else:
    for line in takewhile(illuminacond, af):
        line_split=line.split(',')
        pid=line_split[1][0:3]
        out = line_split[1] + ',' + line_split[2] + ',' + line_split[3][1] + line_split[3][3] + ',' \
                            + line_split[15] + ',' + line_split[9] + ',' + line_split[10]
        if pid!='cnv' and pid!='hCV' and pid!='cnv':
            i = i+1
            bf.write(out.strip('"')+'\n')

Is it possible to compactify this code? If I have some stuff in common in two loops like this, one obvious possibility is to just factor out the common code, but here, eww. The annoying thing is that the only difference here is the writing to c.

Brief summary of code: If K is not None, then loop over K lines of a and write to both b and c. Otherwise, loop over all of a and just write to b.

Answer 1

One check, one loop, no classes, psyco-optimizable.

from itertools import takewhile

if K is None:
    illuminacond = lambda x: x.split(',')[0] != '[Controls]'
    def action(cf, line): cf.write(line)
else:
    illuminacond = lambda x: x.split(',')[0] != '[Controls]' and i < K
    def action(cf, line): pass

af=open('a')
bf=open('b', 'w')
cf=open('c', 'w')

i = 0
for line in takewhile(illuminacond, af):
    line_split=line.split(',')
    pid=line_split[1][0:3]
    out = line_split[1] + ',' + line_split[2] + ',' + line_split[3][1] + line_split[3][3] + ',' \
                              + line_split[15] + ',' + line_split[9] + ',' + line_split[10]
    if pid!='cnv' and pid!='hCV' and pid!='cnv':
        i = i+1
        bf.write(out.strip('"')+'\n')
        action(cf, line)