code: def total_hours(input_files):
      
      hours = 0 
      # Look for singular and plural forms of the word
      # and allow typos.
      allow = set(['hours', 'hour', 'huors', 'huor'])
      for input_file in input_files:
          doc = open(input_file, 'r')
          for line in doc:
              line = line.rstrip()
              data = line.split(' ')
              if (len(data) == 2) and (is_numeric(data[0])) and (data[1].lower() in allow):
                  hours += float(data[0])
          doc.close()
      return hours
docs: Totals the hours for a given projct. Takes a list of input files for 
      which to total the hours. Each input file represents a project.
      There are only multiple files for the same project when the duration 
      was more than a year. A typical entry in an input file might look 
      like this: 
  
      8/24/14
      9:30-12:00 wrote foobar code for x, wrote a unit test for foobar code, tested. 
      2.5 hours
     
      Args:
          input_files: a list of files to parse.
  
      Returns:
          float: the total number of hours spent on the project.