old_contents: #! /usr/bin/env python
  #
  # A module for working with HydroTrend.
  #
  # Mark Piper (mark.piper@colorado.edu)
  
  import numpy as np
  
  
  def load_series(output_file):
      '''
      Reads a column of text containing HydroTrend output. Returns a numpy array,
      or None on an error.
      '''
      try:
          series = np.loadtxt(output_file, skiprows=2)
      except (IOError, StopIteration):
          pass
      else:
          return(series)
  
new_contents: #! /usr/bin/env python
  #
  # A module for working with HydroTrend.
  #
  # Mark Piper (mark.piper@colorado.edu)
  
  from subprocess import call
  import numpy as np
  
  
  def load(output_file):
      '''
      Reads a column of text containing HydroTrend output. Returns a numpy array,
      or None on an error.
      '''
      try:
          series = np.loadtxt(output_file, skiprows=2)
      except (IOError, StopIteration):
          pass
      else:
          return(series)
  
  
  def call(input_dir, output_dir):
      '''
      Invokes HydroTrend through the shell.
      '''
      call(['hydrotrend', '--in-dir', input_dir, '--out-dir', output_dir])
  
subject: Add call() function, rename load() function