在 Python 正则表达式中指定匹配新行的不同方法 [英] Different way to specify matching new line in Python regex

问题描述

我发现在 python 正则表达式中有不同的方法来匹配新行.例如，下面代码中使用的所有模式都可以匹配一个新行

I find out there are different ways to match a new line in python regex. For example, all patterns used in the code below can match a new line

str = 'abc\n123'
pattern = '\n'   # print outputs new line 
pattern2 = '\\n' # print outputs \n
pattern3 = '\\\n' # print outputs \ and new line
pattern4 = r'\n'  # print outputs \n
s = re.search(pattern, str).group()
print ('a' + s + 'a')

我有两个问题:

1. pattern 是一个新行，pattern2 和pattern4 是\n.为什么python regex为不同的字符串生成相同的模式?

1. pattern is a new line, pattern2 and pattern4 is \n. Why python regex generates the same pattern for different string?

不知道为什么 pattern3 也会生成相同的模式.当传递给重新解析器时，pattern3 代表\ + 新行，为什么重新解析器将其翻译成刚好匹配的新行?

Not sure why pattern3 also generates the same pattern. When passed to re parser, pattern3 stands for \ + new line, why re parser translates that into just matching new line?

我使用的是 Python 3

I am using Python 3

推荐答案

组合 \n 表示both Python 本身和 在 re 表达式中也是如此(https://docs.python.org/2.0/ref/strings.html).

The combo \n indicates a 'newline character' in both Python itself and in re expressions as well (https://docs.python.org/2.0/ref/strings.html).

在常规 Python 字符串中，\n 被转换为换行符.换行符 code 然后作为文字字符输入 re 解析器.

In a regular Python string, \n gets translated to a newline. The newline code is then fed into the re parser as a literal character.

Python 字符串中的 双 反斜杠被转换为单个反斜杠.因此，字符串 "\\n" 在内部存储为 "\n"，并且当发送到 re 解析器时，它反过来将这个组合 \n 识别为指示换行代码.

A double backslash in a Python string gets translated to a single one. Therefore, a string "\\n" gets stored internally as "\n", and when sent to the re parser, it in turn recognizes this combo \n as indicating a newline code.

r 符号是防止必须输入双双反斜杠的快捷方式:

The r notation is a shortcut to prevent having to enter double double backslashes:

在前缀为 'r' (https://docs.python.org/2/library/re.html)

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