正则表达式 - 匹配范围

Question

I have the following regular expression:

re.findall(r'(\b[A-Za-z][a-z]{3,10}\b)', string_var)

I expected that this regular expression will return matches with the length ranging from 3 to 10 . It however returns matches for words ranging in length from 4 to 11 .

Do we thus read the above regular expression as matching those words which start with an upper case or lower case letter, followed by letters ranging in length from 3 to 10 ? In other words, having the first letter as the extra letter which extended the range?

Thanks.

Answer 1

Yes.

Your regex is

(\b[A-Za-z][a-z]{3,10}\b)

Now, the grouping parens don't affect the match, so we can ignore them. And the \\b is a "zero-width" matching operator - it matches a transition from one character class to another - so it doesn't actually correspond to any characters. We can ignore them. That leaves this:

[A-Za-z][a-z]{3,10}

This is two character classes, with a repetition specifier suffix on the second:

1. [A-Za-z] - matches one character, upper or lower case Latin alphabetic.

2. [az]{3,10} - matches at least 3, at most 10 characters, lowercase az

So in total, you are matching 1 + [3,10] character. Your minimal match will be 4 characters, and your maximal match will be 11.