我可以编写一个匹配模式的正则表达式，并且该模式的一部分是反向匹配吗？

Question

I want to write a RegEx to remove ellipses from a large text.

I need to find a series of two or more dots, possibly with spaces between them, possibly without. The RegEx I'm using is finding instances of full stops which I don't want to remove, so I want part of the RegEx pattern to negate the pattern if it's followed by a particular string.

I've been using this pattern: re.compile(r'\.[ \.]*\.')

The problem with this is that there are some legitimate abbreviations in the text which are being caught by this.

Take this text for example:

1. Here are ... some . . ellipses..
2. This. . .is ellipsis also.
3. Here is an abbreviation. .i.

In the example above, I want my pattern to find only the ... , . . . . , .. , and . . . . . . in lines 1 and 2. I don't want it to find anything in line 3, however, it will find . . . . in it.

I could update the RegEx to exclude patterns if they're preceded or followed by the letter i like this: re.compile(r'[^i]\.[ \.]*\.'[^i]) but then the pattern won't find the ellipsis in line 2.

Ideally I'd be able to negate a whole sub-string within the pattern so that it won't think . . . . is ellipsis if it's followed by i. or preceded by .i , however, I haven't been able to find any way to do this. Is it possible?

Answer 1

Use negative look ahead and negative look behind:

import re

text = """
1. Here are ... some . . ellipses..
2. This. . .is ellipsis also.
3. Here is an abbreviation. .i.
"""

pattern = re.compile(r'(?<!\.i)\.[ \.]*\.(?!i\.)')
print(pattern.findall(text))   # ['...', '. .', '..', '. . .']
print(pattern.sub('', text))

Text after removing . sequence:

1. Here are  some  ellipses
2. Thisis ellipsis also.
3. Here is an abbreviation. .i.

avoid sequence of . followed by i. you must include another character with i to handle this case:

     . . .is