Question

某些外部代码运行以下代码的功能：

def __init__(self,weights=None,threshold=None):

    print "weights: ", weights
    print "threshold: ", threshold

    if weights:
        print "weights assigned"
        self.weights = weights
    if threshold:
        print "threshold assigned"
        self.threshold = threshold

此代码输出：

weights:  [1, 2]
threshold:  0
weights assigned

即。打印操作符的行为类似threshold为零，而if操作符的行为类似于未定义。

正确的解释是什么？怎么了？ threshold参数的状态是什么以及如何识别它？

Answer 1

使用if weights is not None代替if weights。

更多详细信息：当您说if weights时，您要求Python在布尔上下文中评估weights，并且许多内容可以是“false-equivalent”（或“falsy”），包括{{ 1}}，空字符串，空容器等。如果您只想检查0值，则必须明确地执行此操作。

Answer 2

您可以明确测试None值。

def __init__(self,weights=None,threshold=None):
    print "weights: ", weights
    print "threshold: ", threshold

    if weights is not None:
        print "weights assigned"
        self.weights = weights
    if threshold is not None:
        print "threshold assigned"
        self.threshold = threshold

如何在Python中区分未分配的变量？

2 个答案: