aio-geojson-query 0.0.2

A generalized client for aio-geojson-client

python-aio-geojson-query

This library is my attempt at creating a generalized client for the aio-geojson-client library.

Of course, this requires some uncomfortable contorting as the properties in a GeoJson feed are free-form (see rfc7946)

This is currently under development, so apologies for the bugs.

Installation

pip install aio-geojson-query

Usage

See below for examples of how this library can be used. After instantiating a particular class - feed or feed manager - and supplying the required parameters, you can call update to retrieve the feed data. The return value will be a tuple of a status code and the actual data in the form of a list of feed entries specific to the selected feed.

Status Codes

• OK: Update went fine and data was retrieved. The library may still return empty data, for example because no entries fulfilled the filter criteria.
• OK_NO_DATA: Update went fine but no data was retrieved, for example because the server indicated that there was not update since the last request.
• ERROR: Something went wrong during the update

Parameters

Parameter	Description
home_coordinates	Coordinates (tuple of latitude/longitude)

Supported Filters

Filter		Description
Radius	filter_radius	Radius in kilometers around the home coordinates in which events from feed are included.
Criteria	filter_criteria	Array of filtering conditions.

Criteria Syntax

At this time, criteria are pretty simple and are applied using an oroperator. Therefore, properties matching any function will be a match.

Available operators are: ==, !=, <, >.

The latter two will always compare the property as a float value.

Mappings

Since this library has no knowledge of the feeds being retrieved, this is used to map property names. Mappings are passed as an additional argument called, of course, mappings

Mapping Names

By default, mappings are as simple as: the first argument is known, in the feed, as the second argument.

For instance, let's say you are looking for the date mapping and, in the feed, that field is called published_date -- you will want to help the library find it by passing this mapping:

"date": "published_date"

Parametric Mapping

Sometimes, a value can only be extracted from a complex property. For instance, location may only be available inside the description property. These mappings are denoted using ~~ followed by the regular expression that will extract the value:

"location": "description~~LOCATION: (?P<{}>[^<]+) <br"

Mandatory and default mappings

Some properties are mandatory. For instance, if the library does not find the date property, it will not be able to synchronize the feed properly.

If you do not specify mappings for these variables, the library may attempt to guess what their names could be.

For instance:

Property		Guessed Names
id	Each entry's unique identifier	id, guid (@see FeedManager)
date	Mandatory	time, date
dateformat	A pseudo mapping	Helps the library parse the date property.
description		description, details

Date Parsing

The dateformat pseudo mapping can be:

Format		Meaning
seconds		This is an epoch timestamp,
milliseconds		A timestamp in milliseconds.
An arbitrary string		Used by the library in the strptime function.

Example

I recommend checking out python-aio-geojson-nsw-rfs-incidents which is a library dedicated to retrieving fire incidents information, written by the same author as the library I am creating this middleware for. You may be interested in comparing that library's example code to the one below, which does the same thing (then checks for earthquakes when done):

import asyncio
from aiohttp import ClientSession
from aio_geojson_query import GeoJsonQueryFeed


async def main() -> None:
    async with ClientSession() as websession:
        # NSW Incidents Feed
        # Home Coordinates: Latitude: -33.0, Longitude: 150.0
        # Filter radius: 50 km
        # Filter categories: 'Advice'
        feed = GeoJsonQueryFeed(websession,
                                "https://www.rfs.nsw.gov.au/feeds/majorIncidents.json",
                                (-33.0, 150.0),
                                filter_radius=500,
                                filter_criteria=[
                                    ['category', '==', 'Advice']
                                    ],
                                mappings={
                                    "date": "pubDate",
                                    "location": "description~~LOCATION: (?P<{}>[^<]+) <br"
                                })
        status, entries = await feed.update()
        print(status)
        for entry in entries:
            print("%s [%s]: @%s" % (entry.title, entry.publication_date, entry.location))

        # Earthquakes, magnitude at least 3, around Los Angeles
        feed2 = GeoJsonQueryFeed(websession,
                                "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_month.geojson",
                                (34.052235, -118.243683),
                                filter_criteria=[
                                    ['mag', '>', '3.0']
                                    ],
                                filter_radius=50,
                                mappings={
                                    "dateformat": "milliseconds",
                                    "date": "updated"
                                })
        status, entries = await feed2.update()
        print(status)
        for entry in entries:
            print("%s [%s]: @%s" % (entry.title, entry.publication_date, entry.title))


asyncio.get_event_loop().run_until_complete(main())

Feed Manager

The Feed Manager helps managing feed updates over time, by notifying the consumer of the feed about new feed entries, updates and removed entries compared to the last feed update.

• If the current feed update is the first one, then all feed entries will be reported as new. The feed manager will keep track of all feed entries' external IDs that it has successfully processed.
• If the current feed update is not the first one, then the feed manager will produce three sets:
  • Feed entries that were not in the previous feed update but are in the current feed update will be reported as new.
  • Feed entries that were in the previous feed update and are still in the current feed update will be reported as to be updated.
  • Feed entries that were in the previous feed update but are not in the current feed update will be reported to be removed.
• If the current update fails, then all feed entries processed in the previous feed update will be reported to be removed.

After a successful update from the feed, the feed manager provides two different dates:

• last_update will be the timestamp of the last update from the feed irrespective of whether it was successful or not.
• last_update_successful will be the timestamp of the last successful update from the feed. This date may be useful if the consumer of this library wants to treat intermittent errors from feed updates differently.
• last_timestamp (optional, depends on the feed data) will be the latest timestamp extracted from the feed data. This requires that the underlying feed data actually contains a suitable date. This date may be useful if the consumer of this library wants to process feed entries differently if they haven't actually been updated.

Specify id

When in doubt... make sure you specify a mapping for id -- if only one entry is returned by the feed manager when you expect multiple entries, it is likely that the feed entries are not properly identified. If necessary, specify a mapping for id to a property that is unique to each entry. For instance, in the USGS earthquake feed, such an entry is code.