code: def _get_input_files(cls, input_specification):
          
          if isinstance(input_specification, (basestring, dict)):
              input_specification = [input_specification]
          elif not isinstance(input_specification, list):
              raise ConfigurationError("Input specification must be string, list or dict.")
  
          out = []
          for input_unit in input_specification:
              if isinstance(input_unit, basestring):
                  out.append(input_unit)
              elif isinstance(input_unit, dict):
                  missing = object()
                  directory = input_unit.get('dir', missing)
                  dir_pointer = input_unit.get('dir_pointer', missing)
                  if directory is missing and dir_pointer is missing:
                      raise ConfigurationError(
                          'Input directory dict must contain'
                          ' "dir" or "dir_pointer" element (but not both)')
                  if directory is not missing and dir_pointer is not missing:
                      raise ConfigurationError(
                          'Input directory dict must not contain'
                          ' both "dir" and "dir_pointer" elements')
                  if dir_pointer is not missing:
                      directory = cls._get_pointer(dir_pointer)
  
                  out.extend(cls._get_directory_files(
                      directory=directory,
                      pattern=input_unit.get('pattern'),
                      include_dot_files=input_unit.get('include_dot_files', False)))
              else:
                  raise ConfigurationError('Input must only contain strings or dicts')
          return out
docs: Get list of input files according to input definition.
  
          Input definition can be:
  
          - str: specifying a filename
  
          - list of str: specifying list a of filenames
  
          - dict with "dir" and optional "pattern" parameters: specifying the
          toplevel directory under which input files will be sought and an optional
          filepath pattern