re.split（＆＃39; \ n。+＆＃39;，内容）输出意外的[＆＃39;＆＃39;，＆＃39;＆＃39;，＆＃39;＆＃39;，＆ ＃39;＆＃39;，＆＃39;＆＃39;，＆＃39;＆＃39;，＆＃39; \ n＆＃39;]

Question

假设有以下文字

'\nModels: Introduction to models | Field types | Indexes | Meta options | Model class\nQuerySets: Making queries | QuerySet method reference | Lookup expressions\nModel instances: Instance methods | Accessing related objects\nMigrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations\nAdvanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions\nOther: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features\n'

我想要实现的结果是

['Models: Introduction to models | Field types | Indexes | Meta options | Model class',
 'QuerySets: Making queries | QuerySet method reference | Lookup expressions',
 'Model instances: Instance methods | Accessing related objects',
 'Migrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations',
 'Advanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions',
 'Other: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features',]

我的第一次尝试是：

In [61]: re.split('\n', content)
Out[61]:
['',
 'Models: Introduction to models | Field types | Indexes | Meta options | Model class',
 'QuerySets: Making queries | QuerySet method reference | Lookup expressions',
 'Model instances: Instance methods | Accessing related objects',
 'Migrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations',
 'Advanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions',
 'Other: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features',
 '']

然而，当我尝试

时

In [60]: re.split('\n.+',content)
Out[60]: ['', '', '', '', '', '', '\n']

输出超出我的预期。我无法理解。

在6.2. re—Regular expression operations

中的示例中

re.split(r'\W+', 'Words, words, words.')
outputs ['Words', 'words', 'words', '']
not [',', ',', ',', ' ']
#why
re.split('\n.+',content)
outputs ['', '', '', '', '', '', '\n']

Answer 1

这很明显：\n.+匹配任何以换行符开头，后跟任何类的一个或多个字符的内容，但.将不匹配控制字符（如换行符）。

所以匹配从\n开始，并在下一个\n之前结束一个字符。因此，您的split分隔符都是可见字符，这样的分割将产生空字符串，因为这些空字符串位于分隔符之间。

您的输入字符串以换行符开头和结尾，因此在使用\n拆分后，第一个和最后一个空字符串。将模式修改为

(?<!^)\n(?<!$)

不匹配前导和尾随换行符。这使用负面的lookbehind和lookahead来排除那些第一个和最后一个。

https://regex101.com/r/A2vIbu/1

Answer 2

假设：

>>> txt
'\nModels: Introduction to models | Field types | Indexes | Meta options | Model class\nQuerySets: Making queries | QuerySet method reference | Lookup expressions\nModel instances: Instance methods | Accessing related objects\nMigrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations\nAdvanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions\nOther: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features\n'

你可以这样做（我将其格式化为你想要的例子......）：

>>> [e for e in txt.split('\n') if e]
['Models: Introduction to models | Field types | Indexes | Meta options | Model class', 
 'QuerySets: Making queries | QuerySet method reference | Lookup expressions', 
 'Model instances: Instance methods | Accessing related objects', 'Migrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations', 
 'Advanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions', 
 'Other: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features']

同样的方法适用于re.split：

>>> [e for e in re.split('\n+',txt) if e]
# same output...

或者，你可以捕捉到你想要的东西，然后分裂你不想要的东西。在这种情况下，请使用后视查找\n之后的文本：

>>> re.findall(r'(?<=\n)([^\n]+)', txt)
# same output

Answer 3

如垃圾收集器所提到的，您第一次尝试的问题是您的原始文本被\n包围，所以在拆分时，您会得到一个空字符串作为表示此事实的第一个元素，同样到最后。

要解决这个问题，首先需要删除那些可以使用.strip方法轻松完成的内容：

>>> import re
>>> t = "\na a a\nb b b\nc c c\n"
>>> t.strip()
'a a a\nb b b\nc c c'
>>> re.split("\n",t.strip())
['a a a', 'b b b', 'c c c']
>>> 

对于此描述的任务，您不需要re模块，str class附带了大量方法来处理各种常见情况，{{3} }方法也会这样做

>>> t.strip().splitlines()
['a a a', 'b b b', 'c c c']
>>> 

Answer 4

我认为您可能会对文本中的正则表达式示例感到困惑。正则表达式中的\W+匹配一个或多个非单词字符。所以空格，标点符号等是匹配的。因此re.split会返回单词列表。

要使您的示例正常工作，您只需要删除.*。

e.g。

import re
content = '\nModels: Introduction to models | Field types | Indexes | Meta options | Model class\nQuerySets: Making queries | QuerySet method reference | Lookup expressions\nModel instances: Instance methods | Accessing related objects\nMigrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations\nAdvanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions\nOther: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features\n'

re.split(r'\n',content)

['', 'Models: Introduction to models | Field types | Indexes | Meta options | Model class', 'QuerySets: Making queries | QuerySet method reference | Lookup expressions', 'Model instances: Instance methods | Accessing related objects', 'Migrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations', 'Advanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions', 'Other: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features', '']

另外，如果您知道自己要以\n开始和结束，那么您可以将空白切掉：

re.split(r'\n',content)[1:-1]
['Models: Introduction to models | Field types | Indexes | Meta options | Model class', 'QuerySets: Making queries | QuerySet method reference | Lookup expressions', 'Model instances: Instance methods | Accessing related objects', 'Migrations: Introduction to Migrations | Operations reference | SchemaEditor | Writing migrations', 'Advanced: Managers | Raw SQL | Transactions | Aggregation | Search | Custom fields | Multiple databases | Custom lookups | Query Expressions | Conditional Expressions | Database Functions', 'Other: Supported databases | Legacy databases | Providing initial data | Optimize database access | PostgreSQL specific features']