我使用python 2.7 iter.product生成三个数据集的笛卡尔积。
这与三个嵌套循环相同。然而，在进入循环之前，我想打印标签＆＃34; Fruit Type：＆＃34;和＆＃34;树类型：＆＃34;如果那不清楚我已经把我想要的输出的例子放在下面。
什么是pythonic方式，我可以生成笛卡尔。集合的产品，然后在后期处理中添加标签，但是没有破坏使用itertools减少内存占用的目的？
import itertools
FRUITS=['apple','orange','pear']
TREES=['ash','oak','beech']
ANIMALS=['dog','cat','horse']
def foo(a,b,c):
print "fruit is " + str(a) + ", tree is " + str(b) + ", animal is " + str(c)
[ foo(a,b,c) for a, b, c in itertools.product(FRUITS, TREES, ANIMALS)]
*************************************** Fruit Type: apple *************************************** --------------------------------------- Tree Type: ash --------------------------------------- fruit is apple, tree is ash, animal is dog fruit is apple, tree is ash, animal is cat fruit is apple, tree is ash, animal is horse --------------------------------------- Tree Type: oak --------------------------------------- fruit is apple, tree is oak, animal is dog fruit is apple, tree is oak, animal is cat fruit is apple, tree is oak, animal is horse --------------------------------------- Tree Type: beech --------------------------------------- fruit is apple, tree is beech, animal is dog fruit is apple, tree is beech, animal is cat fruit is apple, tree is beech, animal is horse --------------------------------------- Tree Type: ash --------------------------------------- *************************************** Fruit Type: orange *************************************** --------------------------------------- Tree Type: ash --------------------------------------- fruit is orange, tree is ash, animal is dog fruit is orange, tree is ash, animal is cat fruit is orange, tree is ash, animal is horse --------------------------------------- Tree Type: oak --------------------------------------- fruit is orange, tree is oak, animal is dog fruit is orange, tree is oak, animal is cat fruit is orange, tree is oak, animal is horse --------------------------------------- Tree Type: beech --------------------------------------- fruit is orange, tree is beech, animal is dog fruit is orange, tree is beech, animal is cat fruit is orange, tree is beech, animal is horse *************************************** Fruit Type: pear *************************************** --------------------------------------- Tree Type: ash --------------------------------------- fruit is pear, tree is ash, animal is dog fruit is pear, tree is ash, animal is cat fruit is pear, tree is ash, animal is horse --------------------------------------- Tree Type: oak --------------------------------------- fruit is pear, tree is oak, animal is dog fruit is pear, tree is oak, animal is cat fruit is pear, tree is oak, animal is horse --------------------------------------- Tree Type: beech --------------------------------------- fruit is pear, tree is beech, animal is dog fruit is pear, tree is beech, animal is cat fruit is pear, tree is beech, animal is horse
答案 0 :(得分：1)
这是一种方式：
from itertools import product
FRUITS = ['apple', 'orange', 'pear']
TREES = ['ash', 'oak', 'beech']
ANIMALS = ['dog', 'cat', 'horse']
lst = [(fruit, tree, animal) for fruit, tree in product(FRUITS, TREES)
for animal in ANIMALS]
fmt = 'fruit is {} tree {} is animal is {}'
last_tree_type = None
last_fruit_type = None
for item in lst:
if last_fruit_type != item[0]:
last_fruit_type = item[0]
print(20*'=')
print('fruit type: {}'.format(item[0]))
print(20*'=')
if last_tree_type != item[1]:
last_tree_type = item[1]
print(20*'-')
print('tree type: {}'.format(item[1]))
print(20*'-')
print(fmt.format(*item))
lst包含三元组[('apple', 'ash', 'dog'), ('apple', 'ash', 'cat'), ...];其余的只是字符串的格式。
通常很好的建议来收集您的数据＆＃39;首先，尽可能晚地进行字符串格式化。