# cf.OF_FRACTION

`cf.``OF_FRACTION`(*arg)

  The amount of concurrently open files above which files containing data arrays may be automatically closed.

  The amount is expressed as a fraction of the maximum possible number of concurrently open files.

  Note that closed files will be automatically reopened if subsequently needed by a variable to access its data array.

  See also

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

  Parameters: | arg : float, optional The new fraction (between 0.0 and 1.0). The default is to not change the current behaviour.
  Returns: | out: `float` The value prior to the change, or the current value if no new value was specified.
  Examples: |

      >>> cf.OF_FRACTION()
      0.5
      >>> old = cf.OF_FRACTION(0.33)
      >>> cf.OF_FRACTION(old)
      0.33
      >>> cf.OF_FRACTION()
      0.5

  The fraction may be translated to an actual number of files as follows:

      >>> old = cf.OF_FRACTION(0.75)
      >>> import resource
      >>> max_open_files = resource.getrlimit(resource.RLIMIT_NOFILE)[0]
      >>> threshold = int(max_open_files * cf.OF_FRACTION())
      >>> max_open_files, threshold
      (1024, 768)