code: def allvars(expr):
      r"""Get the list of valid names in the expression.
  
      Parameters
      ----------
      expr : str
          A valid expression conforming to the Variable Definition Language.
  
      Returns
      -------
      vlist : list
          List of valid variable names.
  
      """
      regex = re.compile("\w+")
      items = regex.findall(expr)
      vlist = []
      for item in items:
          if valid_name(item):
              vlist.append(item)
      return vlist
  
imports: from alphapy.alias import get_alias
  from alphapy.frame import Frame
  from alphapy.frame import frame_name
  from alphapy.globals import BSEP, LOFF, ROFF, USEP
  from alphapy.utilities import valid_name
  import builtins
  from collections import OrderedDict
  from importlib import import_module
  import logging
  import numpy
  import pandas
  import parser
  import re
  import sys
label_desc: Use image node_id 2 for calling a global function with example usage: allvars(expr) and returns: vlist