Python non-greedy regexes

Question

How do I make a python regex like "(.*)" such that, given "a (b) c (d) e" python matches "b" instead of "b) c (d" ?

I know that I can use "[^)]" instead of "." , but I'm looking for a more general solution that keeps my regex a little cleaner. Is there any way to tell python "hey, match this as soon as possible"?

Answer 1

You seek the all-powerful *?

From the docs, Greedy versus Non-Greedy

the non-greedy qualifiers *? , +? , ?? , or {m,n}? [...] match as little text as possible.

Answer 2

>>> x = "a (b) c (d) e"
>>> re.search(r"\(.*\)", x).group()
'(b) c (d)'
>>> re.search(r"\(.*?\)", x).group()
'(b)'

According to the docs :

The ' * ', ' + ', and ' ? ' qualifiers are all greedy; they match as much text as possible. Sometimes this behavior isn't desired; if the RE <.*> is matched against ' <H1>title</H1> ', it will match the entire string, and not just ' <H1> '. Adding ' ? ' after the qualifier makes it perform the match in non-greedy or minimal fashion; as few characters as possible will be matched. Using .*? in the previous expression will match only ' <H1> '.

Answer 3

Would not \\\\(.*?\\\\) work? That is the non-greedy syntax.

Answer 4

使用非贪婪匹配是一个好的开始，但我还建议您重新考虑使用.* —— 怎么样？

groups = re.search(r"\([^)]*\)", x)

Answer 5

As the others have said using the ? modifier on the * quantifier will solve your immediate problem, but be careful, you are starting to stray into areas where regexes stop working and you need a parser instead. For instance, the string "(foo (bar)) baz" will cause you problems.

Answer 6

Do you want it to match "(b)"? Do as Zitrax and Paolo have suggested. Do you want it to match "b"? Do

>>> x = "a (b) c (d) e"
>>> re.search(r"\((.*?)\)", x).group(1)
'b'

Answer 7

To start with, I do not suggest using "*" in regexes. Yes, I know, it is the most used multi-character delimiter, but it is nevertheless a bad idea. This is because, while it does match any amount of repetition for that character, "any" includes 0, which is usually something you want to throw a syntax error for, not accept. Instead, I suggest using the + sign, which matches any repetition of length > 1. What's more, from what I can see, you are dealing with fixed-length parenthesized expressions. As a result, you can probably use the {x, y} syntax to specifically specify the desired length.

However, if you really do need non-greedy repetition, I suggest consulting the all-powerful ? . This, when placed after at the end of any regex repetition specifier, will force that part of the regex to find the least amount of text possible.

That being said, I would be very careful with the ? as it, like the Sonic Screwdriver in Dr. Who, has a tendency to do, how should I put it, "slightly" undesired things if not carefully calibrated. For example, to use your example input, it would identify ((1) (note the lack of a second rparen) as a match.