Question

我编写了一个python程序，尝试使用面向对象的编程对我的ml预测进行评分，并且尝试将函数链接在一起。喜欢说：

answers = predictionsGrader().merge_on('PassengerId').compare("Survived_x", "Survived_y").grade()

但是，我的代码开始抛出属性错误的错误。

AttributeError: 'NoneType' object has no attribute 'compare'

试图理解问题所在后，我意识到尽管初始化返回了一个对象，

<class 'predictionsGrader.predictionsGrader'>

初始化后调用的函数（即merge_on函数）返回NoneType

<class 'NoneType'>

请解决问题。这是完整的代码：

import pandas as pd

class predictionsGrader():

    def __init__(self, predictions, target):
        self.correct = []
        self.predictions = predictions
        self.target = target
        return


    def merge_on(self, row):
        self.row = row
        self.md = pd.merge(self.predictions, self.target, on=[self.row])
        return


    def compare(self, predicted_target, confirmed_target):
        self.predicted_target = predicted_target or "predicted_target"
        self.confirmed_target = confirmed_target or "confirmed_target"
        return


    def grade(self):
        for x in range(len(self.md[self.predicted_target])):
            if (self.md[self.predicted_target][x] == self.md[self.confirmed_target][x]):
                self.correct.append("right")
            else:
                self.correct.append("wrong")
        return self.correct

Answer 1

如果您想要这样的流畅接口，则您的方法（__init__除外）需要返回self。

class predictionsGrader():

    def __init__(self, predictions, target):
        self.correct = []
        self.predictions = predictions
        self.target = target

    def merge_on(self, row):
        self.row = row
        self.md = pd.merge(self.predictions, self.target, on=[self.row])
        return self

    def compare(self, predicted_target, confirmed_target):
        self.predicted_target = predicted_target or "predicted_target"
        self.confirmed_target = confirmed_target or "confirmed_target"
        return self

    def grade(self):
        for x in range(len(self.md[self.predicted_target])):
            if (self.md[self.predicted_target][x] == self.md[self.confirmed_target][x]):
                self.correct.append("right")
            else:
                self.correct.append("wrong")
        return self.correct

__init__不应返回任何内容-它是初始化程序，而不是构造函数。

Answer 2

predictionsGrader()与predictionsGrader.__init__()不同。在后台，某些Python魔术将__init__()称为初始化过程的一部分。

为什么初始化函数返回对象类型，而其他函数返回NoneType

2 个答案: