Quickstart

Installation instructions

The package can be installed from the package directory using a simple:

$ pip install .

and similarly a wheel can be created with:

$ pip wheel .

Note

If you already have the C library liberfa on your system, you can use that by setting environment variable PYERFA_USE_SYSTEM_LIBERFA=1.

Testing

For testing, one can install the packages together with its testing dependencies and then test it with:

$ pip install .[test]
$ pytest

Alternatively, one can use tox, which will set up a separate testing environment for you, with:

$ tox -e test

Usage

The package can be imported as erfa which has all ERFA ufuncs wrapped with python code that tallies errors and warnings. Also exposed are the constants defined by ERFA in erfam.h, as well as numpy.dtype corresponding to structures used by ERFA. Examples:

>>> import erfa
>>> erfa.jd2cal(2460000., [0, 1, 2, 3])
(array([2023, 2023, 2023, 2023], dtype=int32),
 array([2, 2, 2, 2], dtype=int32),
 array([24, 25, 26, 27], dtype=int32),
 array([0.5, 0.5, 0.5, 0.5]))
>>> erfa.plan94(2460000., [0, 1, 2, 3], 1)
array([([ 0.09083713, -0.39041392, -0.21797389], [0.02192341, 0.00705449, 0.00149618]),
       ([ 0.11260694, -0.38275202, -0.21613731], [0.02160375, 0.00826891, 0.00217806]),
       ([ 0.13401992, -0.37387798, -0.21361622], [0.0212094 , 0.00947838, 0.00286503]),
       ([ 0.15500031, -0.36379788, -0.21040601], [0.02073822, 0.01068061, 0.0035561 ])],
      dtype={'names':['p','v'], 'formats':[('<f8', (3,)),('<f8', (3,))], 'offsets':[0,24], 'itemsize':48, 'aligned':True})
>>> erfa.dt_pv
dtype([('p', '<f8', (3,)), ('v', '<f8', (3,))], align=True)
>>> erfa.dt_eraLDBODY
dtype([('bm', '<f8'), ('dl', '<f8'), ('pv', [('p', '<f8', (3,)), ('v', '<f8', (3,))])], align=True)
>>> erfa.DAYSEC
86400.0

It is also possible to use the ufuncs directly, though then one has to deal with the warning and error states explicitly. For instance, compare:

>>> erfa.jd2cal(-600000., [0, 1, 2, 3])
Traceback (most recent call last):
...
ErfaError: ERFA function "jd2cal" yielded 4 of "unacceptable date (Note 1)"
>>> erfa.ufunc.jd2cal(-600000., [0, 1, 2, 3])
(array([-1, -1, -1, -1], dtype=int32),
 ...,
 array([-1, -1, -1, -1], dtype=int32))