Question

代码：

import re    
r = re.search("?:((xxxx)|(yyyy)|(zzzz))+", "x = y + z")

错误消息：

D:/FILE_MGMT_PYTHON/ghqer4tqaery.py
Traceback (most recent call last):
  File "D:/FILE_MGMT_PYTHON/ghqer4tqaery.py", line 4, in <module>
    r = re.search("?:((xxxx)|(yyyy)|(zzzz))+", "x = y + z")
  File "C:\Users\Sam\AppData\Local\Programs\Python\Python38-32\lib\re.py", line 199, in search
    return _compile(pattern, flags).search(string)
  File "C:\Users\Sam\AppData\Local\Programs\Python\Python38-32\lib\re.py", line 302, in _compile
    p = sre_compile.compile(pattern, flags)
  File "C:\Users\Sam\AppData\Local\Programs\Python\Python38-32\lib\sre_compile.py", line 764, in compile
    p = sre_parse.parse(p, flags)
  File "C:\Users\Sam\AppData\Local\Programs\Python\Python38-32\lib\sre_parse.py", line 948, in parse
    p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
  File "C:\Users\Sam\AppData\Local\Programs\Python\Python38-32\lib\sre_parse.py", line 443, in _parse_sub
    itemsappend(_parse(source, state, verbose, nested + 1,
  File "C:\Users\Sam\AppData\Local\Programs\Python\Python38-32\lib\sre_parse.py", line 668, in _parse
    raise source.error("nothing to repeat",
re.error: nothing to repeat at position 0

Process finished with exit code 1

Answer 1

正则表达式以?元字符开头。 ?的意思是“前面的事物为零或一遍”。如果将?放在正则表达式的开头，则由于错误原因，没有任何内容可以重复零次或多次，因此正则表达式无效。

将正则表达式重新排列为(?:(xxxx)|(yyyy)|(zzzz))+会导致(?:被解释为我不打算使用的捕获组。

Answer 2

?：匹配前置子表达式零次或一次。

这是您想要的吗？

import re    
r = re.search("(?:(x))|(?:(y))|(?:(z))+", "x = y + z")
print(r.groups())  # But re.search() will only return the first successful matched result

或找到方程式中的所有变量？像这样：

import re    
r = re.findall(" *([xyz])+ *", "x = y + z", re.I)
print(r)

在`x = y + z`

2 个答案: