code: def _get_conversion_type(self, convert_to=None):
          '''a helper function to return the conversion type based on user 
             preference and input recipe.
  
             Parameters
             ==========
             convert_to: a string either docker or singularity (default None)
  
          '''
          acceptable = ['singularity', 'docker']
  
          # Default is to convert to opposite kind
          conversion = "singularity"
          if self.name == "singularity":
              conversion = "docker"
  
          # Unless the user asks for a specific type
          if convert_to is not None and convert_to in acceptable:
              conversion = convert_to
          return conversiof _get_conversion_type(self, convert_to=None):
          '''a helper function to return the conversion type based on user 
             preference and input recipe.
  
             Parameters
             ==========
             convert_to: a string either docker or singularity (default None)
  
          '''
          acceptable = ['singularity', 'docker']
  
          # Default is to convert to opposite kind
          conversion = "singularity"
          if self.name == "singularity":
              conversion = "docker"
  
          # Unless the user asks for a specific type
          if convert_to is not None and convert_to in acceptable:
              conversion = convert_to
          return conversion
docs: a helper function to return the conversion type based on user 
             preference and input recipe.
  
             Parameters
             ==========
             convert_to: a string either docker or singularity (default None)