regex - Python: Regular expression to match alpha-numeric not working?

Question

I am looking to match a string that is inputted from a website to check if is alpha-numeric and possibly contains an underscore. My code:

if re.match('[a-zA-Z0-9_]',playerName):
            # do stuff

For some reason, this matches with crazy chars for example: nIg○▲ ☆ ★ ◇ ◆

I only want regular A-Z and 0-9 and _ matching, is there something i am missing here?

Answer 1

Python has a special sequence w for matching alphanumeric and underscore when the LOCALE and UNICODE flags are not specified. So you can modify your pattern as,

pattern = '^w+$'