code: def validate_ps_distiller(s):
      if isinstance(s, six.string_types):
          s = s.lower()
      if s in ("none", None):
          return None
      elif s in ("false", False):
          return False
      elif s in ("ghostscript", "xpdf"):
          return s
      else:
          raise ValueError(
              "matplotlibrc ps.usedistiller must either be none, "
              "ghostscript or xpdf"
          )
  
imports: from __future__ import absolute_import, division, print_function
  import six
  from functools import reduce
  import operator
  import os
  import warnings
  import re
  from matplotlib import cbook, testing
  from matplotlib.cbook import mplDeprecation, deprecated, ls_mapper
  from matplotlib.fontconfig_pattern import parse_fontconfig_pattern
  from matplotlib.colors import is_color_like
  from cycler import Cycler, cycler
label_desc: Use image node_id 29 for calling a global function with example usage: validate_ps_distiller(s) and returns: None, False, s