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Simple timeseries data type and field.

Project description

django-simple-timeseries

Serializes small, simple timeseries to a database with Django. Provides the Timeseries class for manipulating timeseries, and the TimeseriesField custom field type for serializing.

Status: Experimental.

Lint status Test status

Example

Define a TimeseriesField on a model:

from django.db import models
from django_simple_timeseries import TimeseriesField

class Appliance(models.Model):
    name = models.CharField(max_length=64)
    temperature = TimeseriesField(
        resolution_seconds=60 * 60,
        max_points=24,
        help_text='Last 24 hours of temperature data',
    )

You can then access Timeseries methods on it:

>>> a = Appliance(name='fridge')
>>> a.temperature.add(23.2)
>>> a.save()
>>> # Wait some time.
>>> a.temperature.add(26.5)
>>> a.save()
>>> print(list(a.iter_points()))
[
    (datetime(2020, 1, 1, 2, 30, 0, tzinfo=<UTC>), 23.2),
    (datetime(2020, 1, 2, 2, 30, 0, tzinfo=<UTC>), 26.5),
]

Requirements

This package supports and is tested against the latest patch versions of:

  • Python: 3.7, 3.8, 3.9
  • Django: 2.2, 3.0, 3.1
  • MariaDB: 10.2, 10.3, 10.4, 10.5
  • MySQL: 5.7, 8.0
  • Oracle: 12.2+ (only tested against 12.2.0.1 SE)
  • PostgreSQL: 9.5, 10, 11, 12
  • SQLite: 3.9.0+

All database backends are tested with the latest versions of their drivers. SQLite is also tested on GitHub Actions' latest macOS and Windows virtual environments.

Installation

pip install django_simple_timeseries

For Django 3.1 and newer, no additional dependencies are required. For earlier versions, this project requires django_jsonfield_backport:

pip install django_jsonfield_backport

How it works

Timeseries

The Timeseries class implements a simple vector-like timeseries. Timeseries data is always contiguous.

Internally, all timeseries instances have:

  • .start_time, a datetime.datetime corresponding to the first data point;
  • .data, the recorded data points (or y-values); and
  • .resolution, a timedelta which describes the fixed interval between samples.

Samples are added by calling the add() method. The add() method ensures contiguousness with the following policy:

  • If fewer than resolution seconds have elapsed since the most recent sample, the most recent sample is replaced.
  • If more than resolution seconds have elapsed since the last sample, the vector is extended by the appropriate number of samples (time_delta % resolution - 1), each which will be recorded as gaps with the value None.
  • In all cases, the vector is trimmed to no more than max_points samples.

TimeseriesField

TimeseriesField is implemented as, and extends, a JSONField. The Timeseries methods .to_object() and .from_object() serialize a Timeseries instance to and from plain python objects, which the custom field type transparently implements.

Usage Notes

This module is experimental and hasn't been exhaustively tested. It is not intended for large timeseries. Use at your own risk!

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