code: def append(self, filename_in_zip, file_contents):
          '''
          Appends a file with name filename_in_zip and contents of
          file_contents to the in-memory zip.
          '''
          # Set the file pointer to the end of the file
          self.in_memory_zip.seek(-1, io.SEEK_END)
  
          # Get a handle to the in-memory zip in append mode
          zf = zipfile.ZipFile(self.in_memory_zip, "a", zipfile.ZIP_DEFLATED, False)
  
          # Write the file to the in-memory zip
          zf.writestr(filename_in_zip, file_contents)
  
          # Mark the files as having been created on Windows so that
          # Unix permissions are not inferred as 0000
          for zfile in zf.filelist:
              zfile.create_system = 0
  
          # Close the ZipFile
          zf.close()
  
          # Rewind the file
          self.in_memory_zip.seek(0)
  
          return self append(self, filename_in_zip, file_contents):
          '''
          Appends a file with name filename_in_zip and contents of
          file_contents to the in-memory zip.
          '''
          # Set the file pointer to the end of the file
          self.in_memory_zip.seek(-1, io.SEEK_END)
  
          # Get a handle to the in-memory zip in append mode
          zf = zipfile.ZipFile(self.in_memory_zip, "a", zipfile.ZIP_DEFLATED, False)
  
          # Write the file to the in-memory zip
          zf.writestr(filename_in_zip, file_contents)
  
          # Mark the files as having been created on Windows so that
          # Unix permissions are not inferred as 0000
          for zfile in zf.filelist:
              zfile.create_system = 0
  
          # Close the ZipFile
          zf.close()
  
          # Rewind the file
          self.in_memory_zip.seek(0)
  
          return self
docs: Appends a file with name filename_in_zip and contents of
          file_contents to the in-memory zip.