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Karoo Array Telescope - Telescope State Client

Project description

This is a client package that allows connection to the Redis database that stores telescope state information for the Science Data Processor of the MeerKAT radio telescope.

The Redis database acts as a key-value store. Each key is either a sensor or an attribute. A sensor has multiple timestamped values organised into an ordered set. An attribute (or immutable key) has a single value without a timestamp that is not allowed to change.

The keys are strings and values are arbitrary Python objects stored as pickles. Keys can be accessed using attribute syntax or dict syntax.

Getting Started

You will need a relatively recent version of Redis installed (2.8.9 or newer).

  • macOS: brew install redis

  • Ubuntu: apt-get install redis-server

Then pip install katsdptelstate and run a local redis-server. If you also want to load RDB files, do pip install katsdptelstate[rdb].

A Simple Example

import time
import katsdptelstate

# Connect to an actual Redis server
telstate = katsdptelstate.TelescopeState('localhost:6379')
# Or use a fake Redis instance (key/values stored in memory, useful for testing)
telstate = katsdptelstate.TelescopeState()
# Load dump file into Redis if katsdptelstate is installed with [rdb] option

# Attribute / dict style access returns the latest value
telstate.add('n_chans', 32768)

# List all keys (attributes and sensors)

# Sensors are timestamped underneath
st = time.time()
telstate.add('n_chans', 4096)
et = time.time()
telstate.add('n_chans', 16384)
# Time ranges can be used and are really fast
telstate.get_range('n_chans', st=st, et=et)
# Add an item 10 seconds back
telstate.add('n_chans', 1024, ts=time.time() - 10)

# Attributes cannot be changed (only deleted)
telstate.add('no_change', 1234, immutable=True)
# Adding it again is OK as long as the value doesn't change
telstate.add('no_change', 1234, immutable=True)
# Will raise katsdptelstate.ImmutableKeyError
telstate.add('no_change', 456)

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