不正确地替换内容

Question

我试着用包含以下单词的句子来替换“早午餐”这个词：星期六、星期天和/或周末。然而，它取代了整个句子，而不仅仅是早午餐这个词

>>> reg = re.compile(r'(?:(?:^|\.)[^.]*(?=saturday|sunday|weekend)[^.]*(brunch)[^.]*(?:\$|\.)|(?:^|\.)[^.]*(brunch)[^.]*(?=saturday|sunday|weekend)[^.]*(?:\$|\.))',re.I)
>>> str = 'Limit 1 per person. Limit 1 per table. Not valid for carryout. Not valid 
    with any other offers, no cash back. Valid only for Wednesday-Friday dinner and 
    Saturday-Sunday brunch. Not valid on federal holidays. Reservation required.'
>>> reg.findall(str)
[('brunch', '')]
>>> reg.sub(r'BRUNCH',str)
'Limit 1 per person. Limit 1 per table. Not valid for carryout. Not valid with any 
 other offers, no cash backBRUNCH Not valid on federal holidays. Reservation required.'

我希望它能产生以下效果：

Limit 1 per person. Limit 1 per table. Not valid for carryout. Not valid with any other
offers, no cash back. Valid only for Wednesday-Friday dinner and Saturday-Sunday BRUNCH. 
Not valid on federal holidays. Reservation required.

回答：

为了解决这个问题，我可以使用以下方法：

>>> reg = re.compile(r'(?:((?:^|\.)[^.]*(?=saturday|sunday|weekend)[^.]*)(brunch)([^.]*(?:\$|\.))|((?:^|\.)[^.]*)(brunch)([^.]*(?=saturday|sunday|weekend)[^.]*(?:\$|\.)))',re.I)
>>> reg.sub('\g<1>BRUNCH\g<3>',str)
'Limit 1 per person. Limit 1 per table. Not valid for carryout. Not valid with any other offers, no cash back. Valid only for Wednesday-Friday dinner and Saturday-Sunday BRUNCH. Not valid on federal holidays. Reservation required.'

Answer 1

保持regex的简单性，使用back引用替换：

reg = re.compile(r'((?:saturday|sunday|weekend)\s+)brunch', re.I)
reg.sub(r'\1BRUNCH',str)
'Limit 1 per person. Limit 1 per table. Not valid for carryout. Not valid with any other
 offers, no cash back. Valid only for Wednesday-Friday dinner and Saturday-Sunday BRUNCH.
 Not valid on federal holidays. Reservation required.'

Answer 2

既然你被迫使用正则表达式：

搜索

((?:^|\.)(?=[^.]*(?:saturday|sunday|weekend))[^.]*)brunch

替换为

\1BRUNCH

确保编译时不区分大小写。见demo

请注意，这只替换每个句子出现一次brunch

Answer 3

与其使用正则表达式，不如将其分解为以下步骤：

s = "Limit 1 per person. Limit 1 per table. Not valid for carryout. Not valid with any other offers, no cash back. Valid only for Wednesday-Friday dinner and Saturday-Sunday brunch. Not valid on federal holidays. Reservation required."
results = []
for line in s.split("."):
    if any(text in line.lower() for text in ("saturday", "sunday", "weekend")):
        results.append(line.replace("brunch", "BRUNCH"))
    else:
        results.append(line)
result = ".".join(results)
print(result)