Nominatim/docs/library/Getting-Started.md

Getting Started

The Nominatim search frontend can directly be used as a Python library in scripts and applications. When you have imported your own Nominatim database, then it is no longer necessary to run a full web service for it and access the database through http requests. There are also less constraints on the kinds of data that can be accessed. The library allows to get access to more detailed information about the objects saved in the database.

!!! danger The library interface is currently in an experimental stage. There might be some smaller adjustments to the public interface until the next version.

The library also misses a proper installation routine, so some manipulation
of the PYTHONPATH is required. At the moment, use is only recommended for
developers with some experience in Python.

Installation

To use the Nominatim library, you need access to a local Nominatim database. Follow the installation and import instructions to set up your database.

It is not yet possible to install it in the usual way via pip or inside a virtualenv. To get access to the library you need to set an appropriate PYTHONPATH. With the default installation, the python library can be found under /usr/local/share/nominatim/lib-python. If you have installed Nominatim under a different prefix, adapt the /usr/local/ part accordingly. You can also point the PYTHONPATH to the Nominatim source code.

A simple search example

To query the Nominatim database you need to first set up a connection. This is done by creating an Nominatim API object. This object exposes all the search functions of Nominatim that are also known from its web API.

This code snippet implements a simple search for the town of 'Brugge':

!!! example === "NominatimAPIAsync" ``` python from pathlib import Path import asyncio

    import nominatim.api as napi

    async def search(query):
        api = napi.NominatimAPIAsync(Path('.'))

        return await api.search(query)

    results = asyncio.run(search('Brugge'))
    if not results:
        print('Cannot find Brugge')
    else:
        print(f'Found a place at {results[0].centroid.x},{results[0].centroid.y}')
    ```

=== "NominatimAPI"
    ``` python
    from pathlib import Path

    import nominatim.api as napi

    api = napi.NominatimAPI(Path('.'))

    results = api.search('Brugge')

    if not results:
        print('Cannot find Brugge')
    else:
        print(f'Found a place at {results[0].centroid.x},{results[0].centroid.y}')
    ```

The Nominatim library is designed around asyncio. NominatimAPIAsync provides you with an interface of coroutines. If you have many requests to make, coroutines can speed up your applications significantly.

For smaller scripts there is also a synchronous wrapper around the API. By using NominatimAPI, you get exactly the same interface using classic functions.

The examples in this chapter will always show-case both implementations. The documentation itself will usually refer only to 'Nominatim API class' when both flavours are meant. If a functionality is available only for the synchronous or asynchronous version, this will be explicitly mentioned.

Defining which database to use

The Configuration section explains how Nominatim is configured using the dotenv library. The same configuration mechanism is used with the Nominatim API library. You should therefore be sure you are familiar with the section.

The constructor of the 'Nominatim API class' takes one mandatory parameter: the path to the project directory. You should have set up this directory as part of the Nominatim import. Any configuration found in the .env file in this directory will automatically used.

You may also configure Nominatim by setting environment variables. Normally, Nominatim will check the operating system environment. This can be overwritten by giving the constructor a dictionary of configuration parameters.

Let us look up 'Brugge' in the special database named 'belgium' instead of the standard 'nominatim' database:

!!! example === "NominatimAPIAsync" ``` python from pathlib import Path import asyncio

    import nominatim.api as napi

    config_params = {
        'NOMINATIM_DATABASE_DSN': 'pgsql:dbname=belgium'
    }

    async def search(query):
        api = napi.NominatimAPIAsync(Path('.'), environ=config_params)

        return await api.search(query)

    results = asyncio.run(search('Brugge'))
    ```

=== "NominatimAPI"
    ``` python
    from pathlib import Path

    import nominatim.api as napi

    config_params = {
        'NOMINATIM_DATABASE_DSN': 'pgsql:dbname=belgium'
    }

    api = napi.NominatimAPI(Path('.'), environ=config_params)

    results = api.search('Brugge')
    ```

Presenting results to humans

All search functions return the raw results from the database. There is no full human-readable label. To create such a label, you need two things:

• the address details of the place
• adapt the result to the language you wish to use for display

Again searching for 'Brugge', this time with a nicely formatted result:

!!! example === "NominatimAPIAsync" ``` python from pathlib import Path import asyncio

    import nominatim.api as napi

    async def search(query):
        api = napi.NominatimAPIAsync(Path('.'))

        return await api.search(query, address_details=True)

    results = asyncio.run(search('Brugge'))

    locale = napi.Locales(['fr', 'en'])
    for i, result in enumerate(results):
        address_parts = result.address_rows.localize(locale)
        print(f"{i + 1}. {', '.join(address_parts)}")
    ```

=== "NominatimAPI"
    ``` python
    from pathlib import Path

    import nominatim.api as napi

    api = napi.NominatimAPI(Path('.'))

    results = api.search('Brugge', address_details=True)

    locale = napi.Locales(['fr', 'en'])
    for i, result in enumerate(results):
        address_parts = result.address_rows.localize(locale)
        print(f"{i + 1}. {', '.join(address_parts)}")
    ```

To request information about the address of a result, add the optional parameter 'address_details' to your search:

>>> results = api.search('Brugge', address_details=True)

An additional field address_rows will set in results that are returned. It contains a list of all places that make up the address of the place. For simplicity, this includes name and house number of the place itself. With the names in this list it is possible to create a human-readable description of the result. To do that, you first need to decide in which language the results should be presented. As with the names in the result itself, the places in address_rows contain all possible name translation for each row.

The library has a helper class Locale which helps extracting a name of a place in the preferred language. It takes a single parameter with a list of language codes in the order of preference. So

locale = napi.Locale(['fr', 'en'])

creates a helper class that returns the name preferably in French. If that is not possible, it tries English and eventually falls back to the default name or ref.

The Locale object can be applied to a name dictionary to return the best-matching name out of it:

>>> print(locale.display_name(results[0].names))
'Brugges'

The address_row field has a helper function to apply the function to all its members and save the result in the local_name field. It also returns all the localized names as a convenient simple list. This list can be used to create a human-readable output:

>>> address_parts = results[0].address_rows.localize(locale)
>>> print(', '.join(address_parts))
Bruges, Flandre-Occidentale, Flandre, Belgique

This is a fairly simple way to create a human-readable description. The place information in address_rows contains further information about each place. For example, which OSM adlin_level was used, what category the place belongs to or what rank Nominatim has assigned. Use this to adapt the output to local address formats.

For more information on address rows, see detailed address description.