python - Python 和 Rubular 之间正则表达式的区别？

Question

在 Rubular 中，我创建了一个正则表达式:

(Prerequisite|Recommended): (\w|-| )*

它与粗体匹配:

Recommended: good comfort level with computers and some of the arts.

Summer. 2 credits. Prerequisite: pre-freshman standing or permission of instructor. Credit may not be applied toward engineering degree. S-U grades only.

以下是 Python 中正则表达式的使用:

note_re = re.compile(r'(Prerequisite|Recommended): (\w|-| )*', re.IGNORECASE)

def prereqs_of_note(note):
    match = note_re.match(note)
    if not match:
        return None
    return match.group(0) 

不幸的是，代码返回 None 而不是匹配项:

>>> import prereqs

>>> result  = prereqs.prereqs_of_note("Summer. 2 credits. Prerequisite: pre-fres
hman standing or permission of instructor. Credit may not be applied toward engi
neering degree. S-U grades only.")

>>> print result
None

我在这里做错了什么？

更新:我需要 re.search() 而不是 re.match() 吗？

Answer 1

您想要使用re.search()，因为它会扫描字符串。您不需要 re.match() 因为它尝试在字符串的开头应用模式。

>>> import re
>>> s = """Summer. 2 credits. Prerequisite: pre-freshman standing or permission of instructor. Credit may not be applied toward engineering degree. S-U grades only."""
>>> note_re = re.compile(r'(Prerequisite|Recommended): ([\w -]*)', re.IGNORECASE)
>>> note_re.search(s).groups()
('Prerequisite', 'pre-freshman standing or permission of instructor')

此外，如果您想匹配“instructor”一词后面的第一个句点，则必须添加一个文字“.”。进入你的模式:

>>> re.search(r'(Prerequisite|Recommended): ([\w -\.]*)', s, re.IGNORECASE).groups()
('Prerequisite', 'pre-freshman standing or permission of instructor. Credit may not be applied toward engineering degree. S-U grades only.')

我建议你让你的模式更加贪婪并匹配该行的其余部分，除非这不是你真正想要的，尽管看起来你确实想要。

>>> re.search(r'(Prerequisite|Recommended): (.*)', s, re.IGNORECASE).groups()
('Prerequisite', 'pre-freshman standing or permission of instructor. Credit may not be applied toward engineering degree. S-U grades only.')

前面的模式添加了文字“.”，返回的结果与本示例中的 .* 相同。