class_docstr: A dictionary which represents a model-theoretic Valuation of non-logical constants.
  Keys are strings representing the constants to be interpreted, and values correspond
  to individuals (represented as strings) and n-ary relations (represented as sets of tuples
  of strings).
  
  An instance of ``Valuation`` will raise a KeyError exception (i.e.,
  just behave like a standard  dictionary) if indexed with an expression that
  is not in its list of symbols.
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docstr: The non-logical constants which the Valuation recognizes.
docstr_tok: ["The","non-logical","constants","which","the","Valuation","recognizes","."]
code: def symbols(self):
      """The non-logical constants which the Valuation recognizes."""
      return sorted(self.keys())
  
imports: import inspect
  import re
  import sys
  import textwrap
  from pprint import pformat
  from nltk.decorators import decorator
  from nltk.sem.logic import AbstractVariableExpression, AllExpression, AndExpression, ApplicationExpression, EqualityExpression, ExistsExpression, Expression, IffExpression, ImpExpression, IndividualVariableExpression, IotaExpression, LambdaExpression, NegatedExpression, OrExpression, Variable, is_indvar
label_desc: Use image node_id 5 for calling the Valuation obj's underlying member method code with example usage: obj.symbols() and returns: sorted