Quick-Start#

asdf-astropy is an extension library for ASDF enabling saving and loading many astropy objects. No additional setup is needed, just install asdf-astropy to start saving and loading astropy objects to ASDF files.

A quick example of ASDF#

The Advanced Scientific Data Format (ASDF, pronounced “Az-diff”) is a next-generation interchange format for scientific data. The Python library asdf can be used to read and write ASDF files and provides an interface to the ASDF “tree” that is similar to a python dictionary, with key/value pairs.

To save a Gaussian1D model in an ASDF file:

from asdf import AsdfFile
from astropy.modeling.models import Gaussian1D

# Create a Gaussian1D model
model = Gaussian1D(amplitude=10.4, mean=3.2, stddev=0.1)

# Create a tree structure for the ASDF file, and write it.
tree = {'gaussian_model': model}
ff = AsdfFile(tree)
ff.write_to("hello_world.asdf")

# One can also create the file first, and then modify it directly.
ff = AsdfFile()
ff.tree['gaussian_model'] = model
ff.write_to("hello_world.asdf")

To open the existing file one can use the top-level asdf.open method directly or as a context manager:

import asdf

ff = asdf.open("hello_world.asdf")

# As a context manager
with asdf.open("hello_world.asdf") as ff:
    ...

In either case the file ff will be an asdf.AsdfFile object which is accessible just like a Python dictionary. ASDF will fully realize all of the objects stored within the file automatically. For example, to access the model stored in the file ff['gaussian_model'] will be a Gaussian1D object exactly matching the model written originally.

One can also update an existing file. For example, if one wanted to update the hello_world.asdf file with a SkyCoord object:

import asdf
from astropy import units as u
from astropy.coordinates import SkyCoord

# Create a SkyCoord object
coord = SkyCoord(ra=10.625*u.degree, dec=41.2*u.degree, frame='icrs')

with asdf.open("hello_world.asdf", mode='rw') as af:
    af.tree['skycoord'] = coord
    af.update()

In the same way that the Gaussian1D model round-tripped, the SkyCoord object will also round-trip.

Quick-Start#

A quick example of ASDF#

Further Reading#