# cf.open_files

`cf.``open_files`(file_format=None)

  Return the open files containing sub-arrays of master data arrays.

  By default all such files are returned, but the selection may be restricted to files of a particular format.

  See also

  `cf.close_files`, `cf.close_one_file`, `cf.open_files_threshold_exceeded`

  Parameters: | file_format : str, optional Only return files of the given format. Recognised formats are `'netCDF'` and `'PP'`. By default all files are returned.
  Returns: | out: `dict` If file_format is set then return a dictionary of file names of the specified format and their open file objects. If file_format is not set then return a dictionary for which each key is a file format whose value is the dictionary that would have been returned if the file_format parameter was set.
  Examples: |

      >>> cf.open_files()
      {'netCDF': {'file1.nc': <netCDF4.Dataset at 0x187b6d0>}}
      >>> cf.open_files('netCDF')
      {'file1.nc': <netCDF4.Dataset at 0x187b6d0>}
      >>> cf.open_files('PP')
      {}