Nominatim/docs/develop/ICU-Tokenizer-Modules.md

Writing custom sanitizer and token analysis modules for the ICU tokenizer

The ICU tokenizer provides a highly customizable method to pre-process and normalize the name information of the input data before it is added to the search index. It comes with a selection of sanitizers and token analyzers which you can use to adapt your installation to your needs. If the provided modules are not enough, you can also provide your own implementations. This section describes how to do that.

Using non-standard sanitizers and token analyzers

Sanitizer names (in the step property) and token analysis names (in the analyzer) may refer to externally supplied modules. There are two ways to include external modules: through a library or from the project directory.

To include a module from a library, use the absolute import path as name and make sure the library can be found in your PYTHONPATH.

To use a custom module without creating a library, you can put the module somewhere in your project directory and then use the relative path to the file. Include the whole name of the file including the .py ending.

Custom sanitizer modules

A sanitizer module must export a single factory function create with the following signature:

def create(config: SanitizerConfig) -> Callable[[ProcessInfo], None]

The function receives the custom configuration for the sanitizer and must return a callable (function or class) that transforms the name and address terms of a place. When a place is processed, then a ProcessInfo object is created from the information that was queried from the database. This object is sequentially handed to each configured sanitizer, so that each sanitizer receives the result of processing from the previous sanitizer. After the last sanitizer is finished, the resulting name and address lists are forwarded to the token analysis module.

Sanitizer functions are instantiated once and then called for each place that is imported or updated. They don't need to be thread-safe. If multi-threading is used, each thread creates their own instance of the function.

Sanitizer configuration

::: nominatim.tokenizer.sanitizers.config.SanitizerConfig rendering: show_source: no heading_level: 6

The sanitation function

The sanitation function receives a single object with three members:

• place: read-only information about the place being processed. See PlaceInfo below.
• names: The current list of names for the place. Each name is a PlaceName object.
• address: The current list of address names for the place. Each name is a PlaceName object.

While the place member is provided for information only, the names and address lists are meant to be manipulated by the sanitizer. If may add and remove entries, change information within a single entry (for example by adding extra attributes) or completely replace the list with a different one.

PlaceInfo - information about the place

::: nominatim.data.place_info.PlaceInfo rendering: show_source: no heading_level: 6

PlaceName - extended naming information

::: nominatim.tokenizer.sanitizers.base.PlaceName rendering: show_source: no heading_level: 6