字典共享对象之间没有理由？ [英] dictionary shared between objects for no reason?

问题描述

下面的代码应该创建一个新的（修改）版本的频率分布（nltk.FreqDist）。两个变量应该是相同的长度。

The following code is supposed to create a new (modified) version of a frequency distribution (nltk.FreqDist). Both variables should then be the same length.

当创建WebText的单个实例时，它可以正常工作。但是当创建多个WebText实例时，新变量似乎被所有对象共享。

It works fine when a single instance of WebText is created. But when multiple WebText instances are created, then the new variable seems to be shared by all the objects.

例如：

import nltk
from operator import itemgetter

class WebText:

    freq_dist_weighted = {}

    def __init__(self, text):
        tokens = nltk.wordpunct_tokenize(text) #tokenize
        word_count = len(tokens)
        freq_dist = nltk.FreqDist(tokens)


        for word,frequency in freq_dist.iteritems():
            self.freq_dist_weighted[word] = frequency/word_count*frequency
        print len(freq_dist), len(self.freq_dist_weighted)

text1 = WebText("this is a test")
text2 = WebText("this is another test")
text3 = WebText("a final sentence")

会导致

4 4
4 5
3 7

这不正确。因为我只是转置和修改值，每列中应该有相同的数字。
如果我在循环之前重置freq_dist_weighted，它工作正常：

Which is incorrect. Since I am just transposing and modifying values, there should be the same numbers in each column. If I reset the freq_dist_weighted just before the loop, it works fine:

import nltk
from operator import itemgetter

class WebText:

    freq_dist_weighted = {} 

    def __init__(self, text):
        tokens = nltk.wordpunct_tokenize(text) #tokenize
        word_count = len(tokens)
        freq_dist = nltk.FreqDist(tokens)
        self.freq_dist_weighted = {}

        for word,frequency in freq_dist.iteritems():
            self.freq_dist_weighted[word] = frequency/word_count*frequency
        print len(freq_dist), len(self.freq_dist_weighted)

text1 = WebText("this is a test")
text2 = WebText("this is another test")
text3 = WebText("a final sentence")

导致（正确）：

4 4
4 4
3 3

这对我来说没有意义。

This doesn't make sense to me.

我不明白为什么我必须重置它，因为它被隔离在对象中。我做错了什么？

I don't see why I would have to reset it, since it's isolated within the objects. Am I doing something wrong?

推荐答案

您的评论是明显错误的。类范围中的对象仅在创建类时初始化;如果你想为每个实例一个不同的对象，那么你需要将它移动到初始化器。

Your comment is blatantly wrong. Objects in a class scope are only initialized when the class is created; if you want a different object per instance then you need to move it into the initializer.

class WebText:
    def __init__(self, text):
        self.freq_dist_weighted = {} #### RESET the dictionary HERE ####
         ...

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