Custom WTForms Validators written in python

validators.py

def is_phone_number(form, field):
    digits = filter(lambda x: x.isdigit(),field.data)
    if len(digits) != 10 and len(digits) != 7:
        raise validators.ValidationError(u'Invalid phone number')

def is_valid_header(form, field):
    if '\n' in field.data or '\r' in field.data:
        raise validators.ValidationError(u'Email headers cannot contain newlines')