docs: def generate_temporary_file(folder='/tmp', prefix='helpme', ext='json'):
      '''write a temporary file, in base directory with a particular extension.
        
         Parameters
         ==========
         folder: the base directory to write in. 
         prefix: the prefix to use
         ext: the extension to use.
  
      '''        
      tmp = next(tempfile._get_candidate_names())
      return '%s/%s.%s.%s' %(folder, prefix, tmp, ext)