converts 1.8+ illumina qualities somehow to 1.5+

toIllu.py

#!/usr/bin/env python

def toIllu(c):
    """returns the 1.5 value of phred+33
    >>> [toIllu(ord(n)) for n in["!",'"',"#","$","H","I","J"]] 
    ['B', 'B', 'B', 'C', 'g', 'h', 'h']
    """
    if c < 36:
       return "B"
    elif c > 73:
       return "h"
    else:
       return chr(c+31)

def toArray(s):
    """to chr array
    >>> toArray('!"#GHIJ')
    [33, 34, 35, 71, 72, 73, 74]
    """
    return [ord(c) for c in unpack('%sc' % len(s), s)]

import sys
from struct import unpack

def process(infile):
    lineNo = 1
    for line in open(infile):
       if lineNo % 4 == 0 :
          ill = [toIllu(c) for c in toArray(line.strip())]
          print "".join(ill)
       else:
          print(line), 
       lineNo += 1

if __name__ == "__main__":
    if sys.argv[1] == "-v":
       import doctest
       doctest.testmod()
    else:
       process(sys.argv[1])