Overview

Registering a Scalar UDF involves including the specified UDF in the backend database and returning a UDF operator that can be manipulated within the Ibis DataFrame after registration.

The value returned by registering a Scalar UDF is a UDF operator in the DataFrame. This UDF operator can subsequently be invoked multiple times by various DataFrame expressions.

Overall, registering a Scalar UDF can be done in two ways: explicit registration and implicit registration.

**Table 1** Methods for registering a Scalar UDF
Registration Method	Description	Dependent on Session Object	Intrusively Add Registration Logic	Use Case	Helpful Link
Explicit registration	Code explicitly specifies the registration information of the Scalar UDF.	Yes	Yes	If you wish to precisely control the registration timing, allow intrusive addition of registration logic, or require separation between registration and usage of Scalar UDFs under the same backend connection.	Scalar UDF Explicit Registration Syntax
Implicit registration	Automatically discovers and registers Scalar UDFs during runtime.	No	No	If you prefer non-intrusive registration of Scalar UDFs and do not require separation between registration and usage of Scalar UDFs under the same backend connection.	Scalar UDF Implicit Registration Syntax

Whether using explicit or implicit registration, the meaning of registration differs depending on the Scalar UDF type. Details are provided in the table below.

**Table 2** Meanings of registering a Scalar UDF
Scalar UDF Type	Meaning	Helpful Link
python	Registers a raw Python function or class into the database.	Scalar Python UDF Registration Parameters
builtin	Obtains the handle of an existing function in the database; no actual registration operation is performed.	Scalar Builtin UDF Registration Parameters

If a Python class is passed during registration, the __init__, process, and __del__ instance methods have specific semantic interpretations. Details can be found in the table below. There are no restrictions on other Python classes or instance methods, allowing users to freely add them.

**Table 3** Special instance methods when registering a Python class
Python Class Method	Mandatory	Parameter	Description	Use Case
__init__(self, args, *kwargs)	No	Parameters are passed through the with_arguments method. Only scalar values are allowed.	Constructor of the UDF.	Initializes UDF attributes (such as saving parameters, opening files, and establishing connections).
process(self, args, *kwargs)	Yes	Parameters are passed through the UDF operator. Both scalar values and column names are allowed.	Entry point for the service logic of the UDF.	Processes data and performs calculations in the UDF.
__del__(self)	No	Does not support passing parameters.	Destructor of the UDF.	Clears UDF resources (for example, closing files and disconnecting networks).