python-3.x - append() 方法的意外行为。为什么在向列表中添加字典时，列表的先前元素会被覆盖？

Question

以下代码检查新闻文本中是否存在公司名称（来自tickerList）或其片段（来自newsList）。如果在新闻 打印中找到公司时给出了公司的预期股票代码，但是在将此新闻添加到列表后，会发生一些废话:(看起来，当将字典（新闻）附加到列表时（tickersNews )，列表的前面的元素被覆盖了。为什么？

应该注意的是，当作为字典附加的新闻转换为字符串时，一切正常

import re

tickersList = [('ATI', 'Allegheny rporated', 'Allegheny Technologies Incorporated'), ('ATIS', 'Attis', 'Attis Industries, Inc.'), ('ATKR', 'Atkore International Group', 'Atkore International Group Inc.'), ('ATMP', 'Barclays + Select M', 'Barclays ETN+ Select MLP'), ('ATNM', 'Actinium', 'Actinium Pharmaceuticals, Inc.'), ('ATNX', 'Athenex', 'Athenex, Inc.'), ('ATOS', 'Atossa Genetics', 'Atossa Genetics Inc.'), ('ATRA', 'Atara Biotherapeutics', 'Atara Biotherapeutics, Inc.'), ('ATRC', 'AtriCure', 'AtriCure, Inc.'), ('ATRO', 'Astronics', 'Astronics Corporation'), ('ATRS', 'Antares Pharma', 'Antares Pharma, Inc.'), ('ATSG', 'Air Transport Services Group', 'Air Transport Services Group, Inc.'),  ('CJ', 'C&J Energy', 'C&J Energy Services, Inc.'), ('CJJD', 'China Jo-Jo Drugstores', 'China Jo-Jo Drugstores, Inc.'), ('CLAR', 'Clarus', 'Clarus Corporation'), ('CLD', 'Cloud Peak Energy', 'Cloud Peak Energy Inc.'), ('CLDC', 'China Lending', 'China Lending Corporation'), ('CLDR', 'Cloudera', 'Cloudera, Inc.')]

newsList = [
    {'title':'Atara Biotherapeutics Announces Planned Chief Executive Officer Transition'},
    {'title':'Chongqing Jingdong Pharmaceutical and Athenex Announce a Strategic Partnership and Licensing Agreement to Develop and Commercialize KX2-391 in China'}
           ]

tickersNews = []

for news in newsList:
    # pass through the list of companies looking for their mention in the news
    for ticker, company, company_full in tickersList:
        # clear the full name of the company from brackets, spaces, articles,
        # points and commas and save fragments of the full name to the list
        companyFullFragments = company_full.replace(',', '')\
            .replace('.', '').replace('The ', ' ')\
            .replace('(', ' ').replace(')', ' ')\
            .replace('  ', ' ').strip().split()
        # looking for a company in the news every time cutting off
        # the last fragment from the full company name
        for i in range(len(companyFullFragments), 0, -1):
            companyFullFragmentsString = ' '.join(companyFullFragments[:i]).strip()
            lookFor_company = r'(^|\s){0}(\s|$)'.format(companyFullFragmentsString)
            results_company = re.findall(lookFor_company, news['title'])
            # if the title of the news contains the name of the company,
            # then we add the ticker, the found fragment and the full name
            # of the company to the news, print the news and add it to the list
            if results_company:
                news['ticker'] = ticker#, companyFullFragmentsString, company_full
                print(news['ticker'], 'found')
                #tickersNews.append(str(news))
                #-----------------------------Here is the problem!(?)
                tickersNews.append(news)
                # move on to the next company
                break

print(20*'-', 'appended:')
for news in tickersNews:
    print(news['ticker'])

输出（字典列表）：

ATRA found
ATNX found
CJJD found
CLDC found
-------------------- appended:
ATRA
CLDC
CLDC
CLDC

输出（字符串列表）：

ATRA found
ATNX found
CJJD found
CLDC found
-------------------- appended as a strings:
["{'title': 'Atara Biotherapeutics Announces Planned Chief Executive Officer Transition', 'ticker': 'ATRA'}", "{'title': 'Chongqing Jingdong Pharmaceutical and Athenex Announce a Strategic Partnership and Licensing Agreement to Develop and Commercialize KX2-391 in China', 'ticker': 'ATNX'}", "{'title': 'Chongqing Jingdong Pharmaceutical and Athenex Announce a Strategic Partnership and Licensing Agreement to Develop and Commercialize KX2-391 in China', 'ticker': 'CJJD'}", "{'title': 'Chongqing Jingdong Pharmaceutical and Athenex Announce a Strategic Partnership and Licensing Agreement to Develop and Commercialize KX2-391 in China', 'ticker': 'CLDC'}"]

标签： python-3.xlistdictionaryappend

Answer 1

问题源于 2 行：位于 for 循环内news['ticker'] = ticker。tickersNews.append(news)您的问题更简单的版本是：

a = 10
a = 20
a = 30
print(a, a, a)

输出将是30 30 30. 我想这很明显。

要解决问题，您可以使用多种方法。

第一种可能性（最简单）。替换tickersNews.append(news)为tickersNews.append(news.copy())。

第二种可能性（首选）。不要使用tickersNews. 对于每个news创建空列表news['ticker_list'] = list()。对于每个ticker附加到news['ticker_list']：

import re

tickersList = [('ATI', 'Allegheny rporated', 'Allegheny Technologies Incorporated'), ('ATIS', 'Attis', 'Attis Industries, Inc.'), ('ATKR', 'Atkore International Group', 'Atkore International Group Inc.'), ('ATMP', 'Barclays + Select M', 'Barclays ETN+ Select MLP'), ('ATNM', 'Actinium', 'Actinium Pharmaceuticals, Inc.'), ('ATNX', 'Athenex', 'Athenex, Inc.'), ('ATOS', 'Atossa Genetics', 'Atossa Genetics Inc.'), ('ATRA', 'Atara Biotherapeutics', 'Atara Biotherapeutics, Inc.'), ('ATRC', 'AtriCure', 'AtriCure, Inc.'), ('ATRO', 'Astronics', 'Astronics Corporation'), ('ATRS', 'Antares Pharma', 'Antares Pharma, Inc.'), ('ATSG', 'Air Transport Services Group', 'Air Transport Services Group, Inc.'),  ('CJ', 'C&J Energy', 'C&J Energy Services, Inc.'), ('CJJD', 'China Jo-Jo Drugstores', 'China Jo-Jo Drugstores, Inc.'), ('CLAR', 'Clarus', 'Clarus Corporation'), ('CLD', 'Cloud Peak Energy', 'Cloud Peak Energy Inc.'), ('CLDC', 'China Lending', 'China Lending Corporation'), ('CLDR', 'Cloudera', 'Cloudera, Inc.')]

newsList = [
    {'title':'Atara Biotherapeutics Announces Planned Chief Executive Officer Transition'},
    {'title':'Chongqing Jingdong Pharmaceutical and Athenex Announce a Strategic Partnership and Licensing Agreement to Develop and Commercialize KX2-391 in China'}
           ]

for news in newsList:
    news['ticker_list'] = list()
    for ticker, company, company_full in tickersList:
        companyFullFragments = company_full.replace(',', '')\
            .replace('.', '').replace('The ', ' ')\
            .replace('(', ' ').replace(')', ' ')\
            .replace('  ', ' ').strip().split()
        for i in range(len(companyFullFragments), 0, -1):
            companyFullFragmentsString = ' '.join(companyFullFragments[:i]).strip()
            lookFor_company = r'(^|\s){0}(\s|$)'.format(companyFullFragmentsString)
            results_company = re.findall(lookFor_company, news['title'])
            if results_company:
                news['ticker_list'].append(ticker)
                # print(ticker, 'found')
                break

print('tickers for news:')

for news in newsList:
    print(news['ticker_list'])

输出将是：

tickers for news:
['ATRA']
['ATNX', 'CJJD', 'CLDC']