--- title: Expressions --- Expressions allow you to write custom logic using Python code. Expressions are used in different places throughout passbook, and can do different things. :::info These functions/objects are available wherever expressions are used. For more specific information, see [Expression Policies](../policies/expression.md) and [Property Mappings](../property-mappings/expression.md) ::: ## Global objects - `pb_logger`: structlog BoundLogger. ([ref](https://www.structlog.org/en/stable/api.html#structlog.BoundLogger)) - `requests`: requests Session object. ([ref](https://requests.readthedocs.io/en/master/user/advanced/)) ## Generally available functions ### `regex_match(value: Any, regex: str) -> bool` Check if `value` matches Regular Expression `regex`. Example: ```python return regex_match(request.user.username, '.*admin.*') ``` ### `regex_replace(value: Any, regex: str, repl: str) -> str` Replace anything matching `regex` within `value` with `repl` and return it. Example: ```python user_email_local = regex_replace(request.user.email, '(.+)@.+', '') ``` ### `pb_is_group_member(user: User, **group_filters) -> bool` Check if `user` is member of a group matching `**group_filters`. Example: ```python return pb_is_group_member(request.user, name="test_group") ``` ### `pb_user_by(**filters) -> Optional[User]` Fetch a user matching `**filters`. Returns "None" if no user was found. Example: ```python other_user = pb_user_by(username="other_user") ``` ## Comparing IP Addresses To compare IP Addresses or check if an IP Address is within a given subnet, you can use the functions `ip_address('192.0.2.1')` and `ip_network('192.0.2.0/24')`. With these objects you can do [arithmetic operations](https://docs.python.org/3/library/ipaddress.html#operators). You can also check if an IP Address is within a subnet by writing the following: ```python ip_address('192.0.2.1') in ip_network('192.0.2.0/24') # evaluates to True ```