code for Computer Language Shootout

Michael Spencer mahs at
Wed Mar 16 23:27:40 CET 2005

Steven Bethard wrote:
> Michael Spencer wrote:
>> def output(seq, linelength = 60):
>>     if seq:
>>         iterseq = iter(seq)
>>         while iterseq:
>>             print "".join(islice(iterseq,linelength))
> Worth noting: "while iterseq" only works because for this case, you have 
> a list iterator, which provides a __len__ method.  

Thanks! I had noted that the file iterator didn't behave like this, but I hadn't 
  deduced the reason.  Unfortunately, the above construct, while cute, is also 
not terribly speedy.

  >>> print "\n".join(body[-index:-index-linelength:-1]
  ...      for index in xrange(1, len(body), linelength))

is ugly but much faster with an already-existing string

So, my second attempt is:

from itertools import groupby

def revcomp2(input = sys.stdin, linelength = 60):
     basetable = string.maketrans('ACBDGHKMNSRUTWVYacbdghkmnsrutwvy',

     def record(item):
         return item[0] in ">;"

     for header, body in groupby(input, record):
         body = "".join(body)
         if header:
             print body,
             body = body.translate(basetable, "\n\r")
             print "\n".join(body[-index:-index-linelength:-1]
                 for index in xrange(1, len(body), linelength))


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