向空的嵌套列表添加新值

Question

这与How to append to the end of an empty list? 相关，但我还没有足够的声誉在那里发表评论，所以我在这里发布了一个新问题。

我需要将术语附加到一个空的列表列表中。我开始：

Talks[eachFilename][TermVectors]=
      [['paragraph','1','text'],
       ['paragraph','2','text'],
       ['paragraph','3','text']]

我想以

结束

Talks[eachFilename][SomeTermsRemoved]=
      [['paragraph','text'],
       ['paragraph','2'],
       ['paragraph']]

Talks[eachFilename][SomeTermsRemoved] 开始为空。我无法指定我想要的：

Talks[eachFilename][SomeTermsRemoved][0][0]='paragraph'
Talks[eachFilename][SomeTermsRemoved][0][1]='text'
Talks[eachFilename][SomeTermsRemoved][1][0]='paragraph'

等...（IndexError：列表索引超出范围）。如果我强制填充字符串然后尝试更改它，我会得到一个字符串是不可变的错误。

那么，我如何指定我希望Talks[eachFilename][SomeTermsRemoved][0] 为['paragraph','text']，而Talks[eachFilename][SomeTermsRemoved][1] 为['paragraph','2'] 等等？

.append 有效，但只生成一个长列，而不是一组列表。

更具体地说，我有许多在 dict 中初始化的列表

Talks = {}
Talks[eachFilename]= {}
Talks[eachFilename]['StartingText']=[]
Talks[eachFilename]['TermVectors']=[]
Talks[eachFilename]['TermVectorsNoStops']=[]

eachFilename 从文本文件列表中填充，例如：

Talks[eachFilename]=['filename1','filename2']

StartingText 有几行长文本（单个段落）

Talks[filename1][StartingText]=['This is paragraph one','paragraph two']

TermVectors 由 NLTK 包填充，其中包含术语列表，仍分组在原始段落中：

Talks[filename1][TermVectors]=
     [['This','is','paragraph','one'],
      ['paragraph','two']]

我想进一步操作TermVectors，但保留原来的段落列表结构。这将创建一个每行 1 个术语的列表：

for eachFilename in Talks:
    for eachTerm in range( 0, len( Talks[eachFilename]['TermVectors'] ) ):
        for term in Talks[eachFilename]['TermVectors'][ eachTerm ]:
            if unicode(term) not in stop_words:
                Talks[eachFilename]['TermVectorsNoStops'].append( term )

结果（我失去了我的段落结构）：

Talks[filename1][TermVectorsNoStops]=
     [['This'],
      ['is'],
      ['paragraph'],
      ['one'],
      ['paragraph'],
      ['two']]

Answer 1

一些持续的实验以及 cmets 让我朝着解决方案前进。我没有附加每个单独的术语，从而生成一个长列表，而是将术语累积到一个列表中，然后附加每个列表，如下所示：

for eachFilename in Talks:
    for eachTerm in range( 0, len( Talks[eachFilename]['TermVectors'] ) ):
        term_list = [ ]
        for term in Talks[eachFilename]['TermVectors'][ eachTerm ]:
            if unicode(term) not in stop_words:
                term_list.append(term)
        Talks[eachFilename]['TermVectorsNoStops'].append( term )

谢谢大家！

Answer 2

您报告的错误（字符串不可变？）没有任何意义，除非您的列表实际上不是空的但已经填充了字符串。无论如何，如果您从一个空列表开始，那么填充它的最简单方法是添加：

>>> talks = {}
>>> talks['each_file_name'] = {}
>>> talks['each_file_name']['terms_removed'] = []
>>> talks['each_file_name']['terms_removed'].append(['paragraph','text'])
>>> talks['each_file_name']['terms_removed'].append(['paragraph','2'])
>>> talks['each_file_name']['terms_removed'].append(['paragraph'])
>>> talks
{'each_file_name': {'terms_removed': [['paragraph', 'text'], ['paragraph', '2'], ['paragraph']]}}
>>> from pprint import pprint
>>> pprint(talks)
{'each_file_name': {'terms_removed': [['paragraph', 'text'],
                                      ['paragraph', '2'],
                                      ['paragraph']]}}

如果你有一个空列表并尝试使用索引分配给它，它会抛出一个错误：

>>> empty_list = []
>>> empty_list[0] = 10
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: list assignment index out of range

顺便说一句，代码如下：

for eachFilename in Talks:
    for eachTerm in range( 0, len( Talks[eachFilename]['TermVectors'] ) ):
        for term in Talks[eachFilename]['TermVectors'][ eachTerm ]:
            if unicode(term) not in stop_words:
                Talks[eachFilename]['TermVectorsNoStops'].append( term )

与正确的 Python 风格相去甚远。不要使用 camelCase，使用 snake_case。不要大写变量。此外，在您的中级 for 循环中，您使用 for eachTerm in range(0, len(Talks[eachFilename]['TermVectors']，但 eachTerm 是 int，因此使用标准 i j 或 k 更有意义。甚至idx。

无论如何，没有理由让代码变成这样：

Talks[filename1][TermVectors] =
     [['This','is','paragraph','one'],
      ['paragraph','two']] 

进入这个：

Talks[filename1][TermVectors] =
     [['This'],
      ['is'],
      ['paragraph'],
      ['one'],
      ['paragraph'],
      ['two']]

这是一个可重复的示例（我已经为你做了这个，但你应该在发布问题之前自己做这个）：

>>> pprint(talks)
{'file1': {'no_stops': [],
           'term_vectors': [['This', 'is', 'paragraph', 'one'],
                            ['paragraph', 'two']]},
 'file2': {'no_stops': [],
           'term_vectors': [['This', 'is', 'paragraph', 'three'],
                            ['paragraph', 'four']]}}
>>> for file in talks:
...   for i in range(len(talks[file]['term_vectors'])):
...     for term in talks[file]['term_vectors'][i]:
...       if term not in stop_words:
...         talks[file]['no_stops'].append(term)
... 
>>> pprint(file)
'file2'
>>> pprint(talks)
{'file1': {'no_stops': ['This', 'paragraph', 'one', 'paragraph'],
           'term_vectors': [['This', 'is', 'paragraph', 'one'],
                            ['paragraph', 'two']]},
 'file2': {'no_stops': ['This', 'paragraph', 'paragraph', 'four'],
           'term_vectors': [['This', 'is', 'paragraph', 'three'],
                            ['paragraph', 'four']]}}
>>> 

更 Pythonic 的方法如下所示：

>>> pprint(talks)
{'file1': {'no_stops': [],
           'term_vectors': [['This', 'is', 'paragraph', 'one'],
                            ['paragraph', 'two']]},
 'file2': {'no_stops': [],
           'term_vectors': [['This', 'is', 'paragraph', 'three'],
                            ['paragraph', 'four']]}}
>>> for file in talks.values():
...   file['no_stops'] = [[term for term in sub if term not in stop_words] for sub in file['term_vectors']]
... 
>>> pprint(talks)
{'file1': {'no_stops': [['This', 'paragraph', 'one'], ['paragraph']],
           'term_vectors': [['This', 'is', 'paragraph', 'one'],
                            ['paragraph', 'two']]},
 'file2': {'no_stops': [['This', 'paragraph'], ['paragraph', 'four']],
           'term_vectors': [['This', 'is', 'paragraph', 'three'],
                            ['paragraph', 'four']]}}
>>>