My solution to https://gist.github.com/vrybas/ec210d4ee934d26d39c6

complement.rb

class String
  def translate(from_str, to_str)
    IO.popen(["python", "-c", <<-CMD.gsub(/^\s{6}/,"")]) { |f| f.read.chomp }
      import string
      print '#{self}'.translate(string.maketrans('#{from_str}','#{to_str}'))
    CMD
  end
end

class Complement
  def self.of_dna(dna)
    dna.translate('GCTA','CGAU')
  end

  def self.of_rna(rna)
    rna.translate('CGAU','GCTA')
  end
end