Gets a list of the formats a credit card number fits.

def get_format(n):
    """Gets a list of the formats a credit card number fits."""
    formats = []

    if is_visa(n):
        formats.append('visa')
    if is_visa_electron(n):
        formats.append('visa electron')
    if is_mastercard(n):
        formats.append('mastercard')
    if is_amex(n):
        formats.append('amex')
    if is_maestro(n):
        formats.append('maestro')
    if is_discover(n):
        formats.append('discover')

    return formats