Look and Say

las.py

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-
import re

r = re.compile('((\d)\\2*)')
s = '1'
print s
for _ in range(50):
    s = ''.join([''.join([str(len(m[0])), m[0][0]]) for m in r.findall(s)])
    print s

#=> python las.py  3.24s user 0.22s system 43% cpu 7.889 total
# Python 2.7.6

las.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

require 'stringio'

r = /((\d)\2*)/
puts '1'
(2..50).inject('1') do |i, n|
    seq = i.scan(r).inject(StringIO.new) do |s, m|
        s << m[0].length.to_s << m[0][0]
    end
    puts seq.string
    seq.string
end

#=> ruby las.rb  2.96s user 0.12s system 54% cpu 5.642 total
# ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-darwin14]

las2.rb

#!/usr/bin/env ruby
# -*- coding: utf-8 -*-

require 'stringio'

puts '1'
(2..50).inject('1') do |input, n|
  seq = StringIO.new
  last = nil
  count = 0
  input.each_char do |char|
    if last == char
      count += 1
      next
    end
    if not last.nil?
      seq.write(count)
      seq.write(last)
    end
    last = char
    count = 1
  end
  if not last.nil?
    seq.write(count)
    seq.write(last)
  end
  
  puts seq.string
  seq.string
end

#=> ruby las_2.rb  1.64s user 0.05s system 49% cpu 3.418 total
# ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-darwin14]