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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 of type ProcessInfo
which has 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. It 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
Custom token analysis module
Setup of a token analyser is split into two parts: configuration and analyser factory. A token analysis module must therefore implement two functions:
::: nominatim.tokenizer.token_analysis.base.AnalysisModule rendering: show_source: no heading_level: 6
::: nominatim.tokenizer.token_analysis.base.Analyser rendering: show_source: no heading_level: 6