code: def find_filter_class(filtername):
      """Lookup a filter by name. Return None if not found."""
      if filtername in FILTERS:
          return FILTERS[filtername]
      for name, cls in find_plugin_filters():
          if name == filtername:
              return cls
      return None
  
imports: import re
  from pygments.token import String, Comment, Keyword, Name, Error, Whitespace, string_to_tokentype
  from pygments.filter import Filter
  from pygments.util import get_list_opt, get_int_opt, get_bool_opt, get_choice_opt, ClassNotFound, OptionError, text_type, string_types
  from pygments.plugin import find_plugin_filters
label_desc: Use image node_id 1 for calling a global function with example usage: find_filter_class(filtername) and returns: None, FILTERS, cls