sqlalchemy.exc.DontWrapMixin

A mixin class which, when applied to a user-defined Exception class, will not be wrapped inside of .StatementError if the error is emitted within the process of executing a statement.

E.g.:

from sqlalchemy.exc import DontWrapMixin

class MyCustomException(Exception, DontWrapMixin):
    pass

class MySpecialType(TypeDecorator):
    impl = String

    def process_bind_param(self, value, dialect):
        if value == 'invalid':
            raise MyCustomException("invalid!")