如何在Python中实现详细的REGEX

Question

我试图在Python(2.7)中使用详细的正则表达式.如果重要的话,我只是想让它更容易回归,并在未来的某个时候更清楚地理解表达.因为我是新手,所以我首先创建了一个紧凑的表达式,以确保我得到了我想要的东西.

这是紧凑的表达式:

test_verbose_item_pattern = re.compile('\n{1}\b?I[tT][eE][mM]\s+\d{1,2}\.?\(?[a-e]?\)?.*[^0-9]\n{1}')

它按预期工作

这是详细表达式

verbose_item_pattern = re.compile("""
\n{1}       #begin with a new line allow only one new line character
\b?       #allow for a word boundary the ? allows 0 or 1 word boundaries \nITEM or \n  ITEM
I        # the first word on the line must begin with a capital I
[tT][eE][mM]  #then we need one character from each of the three sets this allows for unknown case
\s+       # one or more white spaces this does allow for another \n not sure if I should change it
\d{1,2}    # require one or two digits
\.?        # there could be 0 or 1 periods after the digits 1. or 1
\(?        # there might be 0 or 1 instance of an open paren
[a-e]?      # there could be 0 or 1 instance of a letter in the range a-e
\)?         # there could be 0 or 1 instance of a closing paren
.*          #any number of unknown characters so we can have words and punctuation
[^0-9]     # by its placement I am hoping that I am stating that I do not want to allow strings that end with a number and then \n
\n{1}     #I want to cut it off at the next newline character
""",re.VERBOSE)

问题是,当我运行详细模式时,我得到一个异常

Traceback (most recent call last):
File "C:/Users/Dropbox/directEDGAR-Code-Examples/NewItemIdentifier.py", line 17, in <module>
 """,re.VERBOSE)
 File "C:\Python27\lib\re.py", line 190, in compile
  return _compile(pattern, flags)
 File "C:\Python27\lib\re.py", line 242, in _compile
 raise error, v # invalid expression
 error: nothing to repeat

我担心这会有些愚蠢,但我无法弄明白.我确实采用了我的详细表达并逐行压缩,以确保紧凑版本与详细版本相同.

错误消息表明没有什么可重复的？

Answer 1

• 在定义正则表达式模式时使用原始字符串文字是一个好习惯.许多正则表达式模式使用反斜杠,并且使用原始字符串文字将允许您编写单个反斜杠,而不必担心Python是否会将您的反斜杠解释为具有不同的含义(并且在这些情况下必须使用两个反斜杠) ).

• \b?是无效的正则表达式.这是说0或1字边界.但要么你有一个单词边界,要么你没有.如果你有一个单词边界,那么你有一个单词边界.如果你没有单词边界,那么你有0个单词边界.那么\b?(如果它是有效的正则表达式)总是如此.

• 正则表达式区分字符串的结尾和行的结尾.(一个字符串可能由多行组成.)

  • \A 仅匹配字符串的开头.
  • \Z 仅匹配字符串的结尾.
  • $ 匹配字符串的结尾,以及re.MULTILINE模式中的行尾.
  • ^ 匹配字符串的开头,并在re.MULTILINE模式下开始一行.

import re
verbose_item_pattern = re.compile(r"""
    $            # end of line boundary
    \s{1,2}      # 1-or-2 whitespace character, including the newline
    I            # a capital I
    [tT][eE][mM] # one character from each of the three sets this allows for unknown case
    \s+          # 1-or-more whitespaces INCLUDING newline
    \d{1,2}      # 1-or-2 digits
    [.]?         # 0-or-1 literal .
    \(?          # 0-or-1 literal open paren
    [a-e]?       # 0-or-1 letter in the range a-e
    \)?          # 0-or-1 closing paren
    .*           # any number of unknown characters so we can have words and punctuation
    [^0-9]       # anything but [0-9]
    $            # end of line boundary
    """, re.VERBOSE|re.MULTILINE)

x = verbose_item_pattern.search("""
 Item 1.0(a) foo bar
""")

print(x)

产量

<_sre.SRE_Match object at 0xb76dd020>

(表示匹配)