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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def unique_email_validator(form, field):
 """ Username must be unique. This validator may NOT be customized."""

    user_manager =  current_app.user_manager
    if not user_manager.email_is_available(field.data):
        raise ValidationError(_('This Email is already in use. Please try another one.'))