[英]Can someone explain this program to me?
What does the following expression produce as a value: 以下表达式作为值产生什么:
[(x, x*y) for x in range(2) for y in range(2)]
[(0,0), (0,1), (1,0), (1,1)]
[0, 1, 2]
[(0,0), (1,0), (0,0), (1,1)]
[(0,0), (0,0), (1,0), (1,1)]
None of the above 以上都不是
The answer is 4 , but I don't understand why. 答案是4 ,但我不明白为什么。
read as: 读为:
for x in range(2): # 0,1
for y in range(2): # 0,1
(x, x*y)
Assuming python 2. 假设python 2。
range(2)
returns the list [0, 1]
range(2)
返回列表[0, 1]
[(x, x*y) for x in [0, 1] for y in [0,1]]
Thus x and y will be all combinations of the lists [0, 1]
and [0, 1]
因此,x和y将是列表
[0, 1]
和[0, 1]
[0, 1]
所有组合
[(x, x*y) for (x, y) in [(0, 0), (0, 1), (1, 0), (1, 1)]]
x y x*y (x, x*y)
0 0 0 (0, 0)
0 1 0 (0, 0)
1 0 0 (1, 0)
1 1 1 (1, 1)
Read this as 阅读为
list = [];
for x in range(2):
for y in range(2):
list.append((x, x*y))
Basically it will iterate 4 times with the following X,Y values 基本上它将使用以下X,Y值迭代4次
X=0, Y=0
X=0, Y=1
X=1, Y=0
X=1, Y=1
Zero times anything will always be zero, so you get your 4 arrays 零乘以零将始终为零,因此得到4个数组
First Index = 0, 0*0
Second Index = 0, 0*1
Third Index = 1, 1*0
Fourth Index = 1, 1*1
Nested list comprehensions work in the same way as if you had written for loops like that. 嵌套列表推导的工作方式与您为此类循环编写的方式相同。
So your example list comprehension works like this generator function: 因此,您的示例列表理解类似于此生成器函数:
def example():
for x in range(2):
for y in range(2):
yield (x, x*y)
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