WTForms: Install 'email_validator' for email validation support
From WTForms 2.3.0 version, the email validation is handled by an external library called email-validator (PR #429). If you want to enable email validation support, you either need to install WTForms with extra requires email:
$ pip install wtforms[email]Or you can install email-validator directly:
$ pip install email-validatorOr you can back to the old version of WTForms:
$ pip install wtforms==2.2.1P.S. If you are using Flask-WTF, except for install email-validator directly, you can also use email extra (if PR #423 got merged) in the next release (> 0.14.3).