# Handling phone numbers

Google’s libphonenumber “Falsehoods Programmers Believe About Phone Numbers” are worth keeping in mind, especially since this library relies heavily on libphonenumber.

## About phone numbers extensions

An extension is an additional phone line added to an existing phone system, making it possible to reach a specific employee or department within an organization. An extension is defined in the following manner:

    >>> import phonenumbers
    >>> phonenumbers.parse("+1 604-401-1234 ext. 987")
    PhoneNumber(country_code=1, national_number=6044011234, extension='987', italian_leading_zero=None, number_of_leading_zeros=None, country_code_source=0, preferred_domestic_carrier_code=None)
    >>> phonenumbers.parse("+1 604-401-1234,987")
    PhoneNumber(country_code=1, national_number=6044011234, extension='987', italian_leading_zero=None, number_of_leading_zeros=None, country_code_source=0, preferred_domestic_carrier_code=None)

The library primarily focuses on public phone numbers, its default format and database representation are using E.164, which has no support for extensions.

Projects that need to handle phone number extensions must set both `PHONENUMBER_DEFAULT_FORMAT` and `PHONENUMBER_DB_FORMAT` to an extension-compatible format, as described in Phone number format choices.