code: def coerce_one(schema=str):
      
      def validate(val):
          """Unpack a single item from the inputs sequence and run validation.
  
          NOTE(larsbutler): This code is highly opinionated for bottle, since
          bottle query params are wrapped in a list, even if there is just a
          single value for a given parameter.
          """
          [value] = val
          return volup.Coerce(schema)(value)
      return validate
docs: Expect the input sequence to contain a single value.
  
      :keyword schema:
          Custom schema to apply to the input value. Defaults to just string,
          since this is designed for query params.