code: def reducing(reducer, init=UNSET):
      
  
      reducer2 = reducer
  
      def reducing_transducer(reducer):
          return Reducing(reducer, reducer2, init)
  
      return reducing_transducer
docs: Create a reducing transducer with the given reducer.
  
      Args:
          reducer: A two-argument function which will be used to combine the
              partial cumulative result in the first argument with the next
              item from the input stream in the second argument.
  
      Returns: A reducing transducer: A single argument function which,
          when passed a reducing function, returns a new reducing function
          which entirely reduces the input stream using 'reducer' before
          passing the result to the reducing function passed to the
          transducer.