code: def valid_GC(x):
      
      x = float(x)
      if x < 0.0 or x > 1.0:
          raise ArgumentTypeError("{} not in range [0.0, 1.0]".format(x))
      return x
docs: type function for argparse to check GC values.
  
      Check if the supplied value for minGC and maxGC is a valid input, being between 0 and 1