code: def _validate_linestyle(ls):
      """
      A validator for all possible line styles, the named ones *and*
      the on-off ink sequences.
      """
      # Look first for a valid named line style, like '--' or 'solid'
      if isinstance(ls, six.string_types):
          try:
              return _validate_named_linestyle(ls)
          except (UnicodeDecodeError, KeyError):
              # On Python 2, string-like *ls*, like for example
              # 'solid'.encode('utf-16'), may raise a unicode error.
              raise ValueError(
                  "the linestyle string {!r} is not a valid "
                  "string.".format(ls)
              )
  
      if isinstance(ls, (bytes, bytearray)):
          # On Python 2, a string-like *ls* should already have lead to a
          # successful return or to raising an exception. On Python 3, we have
          # to manually raise an exception in the case of a byte-like *ls*.
          # Otherwise, if *ls* is of even-length, it will be passed to the
          # instance of validate_nseq_float, which will return an absurd on-off
          # ink sequence...
          raise ValueError(
              "linestyle {!r} neither looks like an on-off ink "
              "sequence nor a valid string.".format(ls)
          )
  
      # Look for an on-off ink sequence (in points) *of even length*.
      # Offset is set to None.
      try:
          if len(ls) % 2 != 0:
              raise ValueError(
                  "the linestyle sequence {!r} is not of even "
                  "length.".format(ls)
              )
  
          return (None, validate_nseq_float()(ls))
  
      except (ValueError, TypeError):
          # TypeError can be raised inside the instance of validate_nseq_float,
          # by wrong types passed to float(), like NoneType.
          raise ValueError(
              "linestyle {!r} is not a valid on-off ink "
              "sequence.".format(ls)
          )
  
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 42 for calling a global function with example usage: _validate_linestyle(ls) and returns: None,  validate_nseq_float, _validate_named_linestyle