class_docstr: List of scales
  
  This class has methods the simplify the handling of
  the ggplot object scales
class_docstr_tok: ["List","of","scales","This","class","has","methods","the","simplify","the","handling","of","the","ggplot","object","scales"]
docstr: Add missing but required scales.
  
  Parameters
  ----------
  aesthetics : list | tuple
      Aesthetic names. Typically, ('x', 'y').
docstr_tok: ["Add","missing","but","required","scales",".","Parameters","--","--","--","--","--","aesthetics",":","list","|","tuple","Aesthetic","names",".","Typically",",","(","'","x","'",",","'","y","'",")","."]
code: def add_missing(self, aesthetics):
      """
      Add missing but required scales.
  
      Parameters
      ----------
      aesthetics : list | tuple
          Aesthetic names. Typically, ('x', 'y').
      """
      # Keep only aesthetics that don't have scales
      aesthetics = set(aesthetics) - set(self.input())
  
      for ae in aesthetics:
          scale_name = f"scale_{ae}_continuous"
          scale_f = Registry[scale_name]
          self.append(scale_f())
  
imports: from __future__ import annotations
  import itertools
  import typing
  from contextlib import suppress
  from typing import List
  from warnings import warn
  import numpy
  import pandas.api.types
  from .._utils import array_kind
  from .._utils.registry import Registry
  from ..exceptions import PlotnineError, PlotnineWarning
  from ..mapping.aes import aes_to_scale
  from .scale import scale
label_desc: Use image node_id 17 for calling the Scales obj's underlying member method code with example usage: obj.add_missing(aesthetics) without return types