2.2.2 Hierarchical StructuresをPythonでやってみた

SICPの2.2.2 Hierarchical Structures の Mapping over trees あたりを Python でやってみた

scheme

;2.2.2  Hierarchical Structures
;Mapping over trees
(define (scale-tree tree factor)
  (cond ((null? tree)
         ())
        ((not (pair? tree))
         (* tree factor))
        (else (cons (scale-tree (car tree) factor)
                    (scale-tree (cdr tree) factor)))))
(scale-tree (list 1 (list 2 (list 3 4) 5) (list 6 7))
            10)
;(10 (20 (30 40) 50) (60 70))

(define (scale-tree tree factor)
  (map (lambda (sub-tree)
         (if (pair? sub-tree)
             (scale-tree sub-tree factor)
             (* sub-tree factor)))
       tree))
(scale-tree (list 1 (list 2 (list 3 4) 5) (list 6 7))
            10)
;(10 (20 (30 40) 50) (60 70))

python

scheme の pair?の代用にとりあえず isinstance()をつかってみた。結構ハマった(´･ω･`)
type() でなくてisinstance() 推奨なのね...

#2.2.2  Hierarchical Structures
#Mapping over trees
def scale_tree(tree, factor):
    if not tree:
        return []
    if not isinstance(tree, list):
        return tree * factor
    return [scale_tree(tree[0], factor)] + scale_tree(tree[1:], factor)
print scale_tree([1,[2,[3,4],5],[6,7]], 10)
#[10, [20, [30, 40], 50], [60, 70]]

def scale_tree_lambada(tree, factor):
    return map(lambda sub_tree: isinstance(sub_tree, list) == True
               and scale_tree_lambada(sub_tree, factor) or sub_tree * factor,
               tree)
print scale_tree_lambada([1,[2,[3,4],5],[6,7]], 10)
#[10, [20, [30, 40], 50], [60, 70]]