code: def _get_value(self, key, context):
          
          string_quotes = ('"', "'")
  
          if key[0] in string_quotes and key[-1] in string_quotes:
              return key[1:-1]
          if key in string.digits:
              return int(key)
          return context.get(key, None)
docs: Works out whether key is a value or if it's a variable referencing a
          value in context and returns the correct value.