python中的re.findall（）方法的说明

Question

I wanted to strip a string of punctuation marks and I ended up using

re.findall(r"[\w]+|[^\s\w]", text)

It works fine and it does solve my problem. What I don't understand is the details within the parentheses and the whole pattern thing. What does r"[\\w]+|[^\\s\\w]" really mean? I looked it up in the Python standard library and it says:

re.findall(pattern, string, flags=0)

Return all non-overlapping matches of pattern in string, as a list of strings. The string is scanned left-to-right, and matches are returned in the order found. If one or more groups are present in the pattern, return a list of groups; this will be a list of tuples if the pattern has more than one group. Empty matches are included in the result unless they touch the beginning of another match.

I am not sure if I get this and the clarification sounds a little vague to me. Can anyone please tell me what a pattern in this context means and how exactly it is defined in the findall() method?

Answer 1

To break it down, [] creates a character class . You'll often see things like [abc] which will match a , b or c . Conversely, you also might see [^abc] will will match anything that isn't a , b or c . Finally, you'll also see character ranges: [a-cA-C] . This introduces two ranges and it will match any of a , b , c , A , B , C .

In this case, your character class contains special tokens. \\w and \\s . \\w matches anything letter-like. \\w actually depends on your locale, but it is usually the same thing as [a-zA-Z0-9_] matches anything in the ranges az , AZ , 0-9 or _ . \\s is similar, but it matches anything that can be considered whitespace.

The + means that you can repeat the previous match 1 or more times. so [a]+ will match the entire string aaaaaaaaaaa . In your case, you're matching alphanumeric characters that are next to each other.

the | is basically like "or". match the stuff on the left, or match the stuff on the right if the left stuff doesn't match.

Answer 2

\\w means Alphanumeric characters plus "_". And \\s means Whitespace characters including " \\t\\r\\n\\v\\f" and space character " ". So, [\\w]+|[^\\s\\w] means a string which contains only words and "_".