code: def do_reduce(func_name, *sequence):
      
      if len(sequence)==1:
          sequence = sequence[0]
      return reduce(get_func(func_name), sequence)
docs: Apply a function of two arguments cumulatively to the items of a sequence,
      from left to right, so as to reduce the sequence to a single value.
      
      Functions may be registered with ``native_tags`` 
      or can be ``builtins`` or from the ``operator`` module
      
      Syntax::
      
          {% reduce [function] [sequence] %}        
          {% reduce [function] [item1 item2 ...] %}
      
      For example::
      
          {% reduce add 1 2 3 4 5 %}
          
      calculates::
      
          ((((1+2)+3)+4)+5) = 15