Python 3 正则表达式问题

Question

所以我在 Python 中匹配正则表达式字符串时遇到问题。我已经在 http://regex101.com/ 上测试过它而且效果很好。但是，当我尝试在代码中执行此操作时，它会给出格式错误的正则表达式错误

正则表达式为:“[^\\]\]PW\[”。我想让它找到字符串 ]PW[，只要它前面不以反斜杠开头。代码如下:

import sys,re
fileList = []
if len(sys.argv) == (0 or 1):
    fileList = ['tester.sgf']
else:
    fileList = str(sys.argv)
for sgfName in fileList:
    print(sgfName)
    currentSGF = open(sgfName,'r').read()
    currentSGF = currentSGF.replace("\r","") #clean the string
    currentSGF = currentSGF.replace("\n","")
for iterations in re.finditer("[^\\]\]PW\[",currentSGF): #here's the issue
    print(iterations.start(0), iterations.end(0), iterations.group())

我得到的错误是:

Traceback (most recent call last):
File "C:\Users\Josh\Desktop\New folder\sgflib1.0\test2.py", line 15, in <module>
for iterations in re.finditer("[^\\]\]PW\[",currentSGF):
File "C:\Python33\lib\re.py", line 210, in finditer
  return _compile(pattern, flags).finditer(string)
File "C:\Python33\lib\re.py", line 281, in _compile
  p = sre_compile.compile(pattern, flags)
File "C:\Python33\lib\sre_compile.py", line 491, in compile
  p = sre_parse.parse(p, flags)
File "C:\Python33\lib\sre_parse.py", line 747, in parse
  p = _parse_sub(source, pattern, 0)
File "C:\Python33\lib\sre_parse.py", line 359, in _parse_sub
  itemsappend(_parse(source, state))
File "C:\Python33\lib\sre_parse.py", line 485, in _parse
  raise error("unexpected end of regular expression")
sre_constants.error: unexpected end of regular expression

感谢您的帮助!

Answer 1

您需要使用原始字符串文字或将所有转义符加倍:

re.finditer(r"[^\\]\]PW\[", currentSGF)

或

re.finditer("[^\\\\]\\]PW\\[", currentSGF)

否则，Python 首先将每个转义序列解释为文字字符串值解释的一部分。 re.finditer 看到值 '[^\]]PW[，否则为 \] 和 \[没有特殊意义。

参见The Backslash Plague在 Python 正则表达式 HOWTO 中。