在 Python 中使用正则表达式查找子字符串？

Question

I have A string:

line_to_test = "http://website/[SequenceOfLetters&NumbersONLY].html"

I want a regex for matching the above pattern:

what i have tried currently is:

c = len(re.findall(r"http:\/\/website\/([a-zA-Z0-9]?).html",line_to_test))

But c here comes to be null even when the line_to_test contains the pattern.

Answer 1

? means whatever preceded it was optional, in this case [a-zA-Z0-9] . That means you can have a letter or number either 0 or 1 times.

You should use the * , to select it 0 times or more, or use the + , to select it 1 times` or more.

Try this RegEx:

c = len(re.findall(r"http:\/\/website\/([a-zA-Z0-9]+).html",line_to_test))

If you used a * , it would be the same as ([a-zA-Z0-9]+)? , meaning http://website/.html would work.

Live Demo on RegExr

Answer 2

? will only match 0 or 1 character. Try

c = len(re.findall(r"http:\/\/website\/([a-zA-Z0-9]+).html",line_to_test))

You can use an online service like regexr to test your regexes: http://regexr.com/3d301