Question

在python 2下

    for i in range(6):
        for j in range(i):print i,j

    for i in range(6):
        for j in range(i):
            if j:print i,j

我注意到这两个结果的区别，但我仍然不明白如果j意味着什么。

Answer 1

for i in range(6):
    for j in range(i):
        if j:print i,j

上述if语句确保当j的值为零时不打印i和j。大多数数据类型在Python中都有内部布尔属性。对于数字，任何非零值都会转换为True，而零转换为False

Answer 2

关于真值测试的Python文档：

http://docs.python.org/2/library/stdtypes.html#truth-value-testing

具体做法是：

可以测试任何对象的真值，以便在if或while中使用   条件。以下值被视为false：

任何数字类型的零，例如，0,0L，0.0

所有其他值都被视为真实

if j:将在j为非零时触发，在j为0时不执行任何操作。

Answer 3

要了解if i:中发生的事情，请尝试此操作。

for i in range(-6,6):
    if i:
        print "%2d is evaluated as True"%i
    else:
        print "%2d is evaluated as False"%i

输出：

-6 is evaluated as True
-5 is evaluated as True
-4 is evaluated as True
-3 is evaluated as True
-2 is evaluated as True
-1 is evaluated as True
 0 is evaluated as False    <----- Just "if 0:" is evaluated as "if False:"
 1 is evaluated as True
 2 is evaluated as True
 3 is evaluated as True
 4 is evaluated as True
 5 is evaluated as True

Answer 4

检查j是否为True。数值0被解释为False，而其他每个都被解释为True。

Answer 5

如果j不是假的，则第二个循环是在j上进行调节，即如果j＆gt; 0所以它只打印j不等于0的值

关于if的简单python代码

5 个答案: