Regex Validation With Wtforms And Python

Here is my code: class CreateUser(Form): username = StringField('Username', [ validators.Regexp('\w+', message='Username must contain only letters numbers or underscore

Solution 1:

Replacing the regex with

'^\w+$'

solved the problem.

Solution 2:

I know this was answered a long time ago, but another option I discovered to provide alphanumeric validation on WTForms is AlphaNumeric()

from wtforms_validators import AlphaNumeric
...

class SignupForm(Form):
    login_id = StringField('login Id', [DataRequired(), AlphaNumeric()])

More details here https://pypi.org/project/wtforms-validators/

Solution 3:

@mpn solution works fine but I was wondering why \w+ is not matching the whole string.

In wtforms' Regexp class whitin the method __call__ you will see that self.regex.match(field.data or '') will be called. The documentation of re.py states about re.match that:

If zero or more characters at the beginning of string match the regular expression pattern, return a corresponding match object.

Hence, we will have to use ^ to match the start of the string and $ to match the end of the string. Read more about the special characters in the documentation.