finds top 10 longest line[4]'s using quickselect

top10.py

#!/usr/bin/python
import sys
import csv
import random

# Finds top 10 longest line[4]'s using quickselect sorted in ascending order

def partition(a, l, r, p, key=None):
    pivot_value = key(a[p])
    temp = a[p]
    a[p] = a[r]
    a[r] = temp
    index = l
    for i in xrange(l,r+1):
        if key(a[i]) < pivot_value:
            temp = a[i]
            a[i] = a[index]
            a[index] = temp
    temp = a[r]
    a[r] = a[index]
    a[index] = temp
    return index

def select(a, l, r, n, key=None):
    index = l + int(random.randint(0, r - l))
    index = partition(a, l, r, index, key)
    if index == n:
        return a[:n]
    elif n < index:
        return select(a, l, index - 1, n, key)
    else:
        return select(a, index + 1, r, n, key)

def mapper():
    reader = csv.reader(sys.stdin, delimiter='\t')
    writer = csv.writer(sys.stdout, delimiter='\t', quotechar='"', quoting=csv.QUOTE_ALL)

    test = [(line, len(line[4])) for line in reader]
    top10 = select(test, 0, len(test)-1, 10, key=lambda x: x[1])
    top10.sort(key=lambda x: x[1])
    for line, _ in top10:
        writer.writerow(line)

if __name__ == '__main__':
    import StringIO
    
    test_text = 
    """\"\"\t\"\"\t\"\"\t\"\"\t\"333\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"88888888\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"1\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"11111111111\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"1000000000\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"22\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"4444\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"666666\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"55555\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"999999999\"\t\"\"
    \"\"\t\"\"\t\"\"\t\"\"\t\"7777777\"\t\"\"
    """
    sys.stdin = StringIO.StringIO(test_text)
    mapper()
    sys.stdin = sys.__stdin__