map - 将嵌套的for循环转换为映射等效

Question

示例：

>>>for x in iterable1:
...    expression

地图表格将是：

>>>map(lambda x:expression,iterable1)

如何将此扩展为嵌套？

示例：

>>>for x in itr1:
...    for y in itr2:
...        expr

不使用理解。

编辑：仅使用地图。

Answer 1

您可以使用itertools.product构建两个嵌套序列的笛卡尔积，并将map表达式添加到2元组的列表中：

from itertools import product

map(lambda (x, y): expression, product(itr1, itr2))

一些实际值的示例：

seq = map(lambda (x, y): '%s:%s' % (x, y), product(itr1, itr2))
for item in seq:
    print item

请注意，lambda (x, y)是将序列中的每个2元组解包到表达式中使用的单独x和y参数所必需的。

Answer 2

请耐心等待。不是解释，但这在2天后起作用。仅使用地图和列表。这是糟糕的代码。欢迎提出缩短代码的建议。 Python 3解决方案

使用列表理解的示例：

>>> a=[x+y for x in [0,1,2] for y in [100,200,300]]
>>> a
[100,200,300,101,201,301,102,202,302]

使用示例：

>>>a=[]
>>>for x in [0,1,2]:
...    for y in [100,200,300]:
...        a.append(x+y)
...
>>>a
[100,200,300,101,201,301,102,202,302]

现在仅使用map：

的示例

>>>n=[]
>>>list(map(lambda x:n.extend(map(x,[100,200,300])),map(lambda x:lambda y:x+y,[0,1,2])))
>>>n
[100,200,300,101,201,301,102,202,302]

更小的python2.7解决方案：

>>>m=[]
>>>map(lambda x:m.extend(x),map(lambda x:map(x,[100,200,300]),map(lambda x:lambda y:x+y,[0,1,2])))
>>>m
[100,200,300,101,201,301,102,202,302]

另一种变化：我通过电子邮件发送给Mark Lutz，这是他的解决方案。这不使用闭包，并且最接近嵌套for循环功能。

>>> X = [0, 1, 2]               
>>> Y = [100, 200, 300]
>>> n = []
>>> t = list(map(lambda x: list(map(lambda y: n.append(x + y), Y)),X))
>>> n
[100,200,300,101,201,301,102,202,302]

Answer 3

你不能。 lambda特别限于其返回值可以封装为单个表达式的函数：不允许使用语句。

您应该问自己的一个问题是，为什么您认为这是编写Python程序的理想方式？为了便于阅读，已明确定义了该语言，您应尽一切可能保持该可读性。

Answer 4

Thnks lapin！

我有同样的问题，你给我解决方案：

很长的路：

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简短方法和解决方案：

SUITE = 'Heart Diamonds Spades Clubs'.split()
RANKS = '2 3 4 5 6 7 8 9 10 J Q K A'.split()

for x in RANKS:
    for y in SUITE:
        deck.append(x+" " +y)
print(deck)
print(len(deck))