uttrs 0.1

'uttrs' seeks to interoperate Classes definided using attrs and 'astropy units' in a simple manner.

uttrs

uttrs seeks to interoperate Classes definided using attrs and astropy units in a simple manner.

uttrs is mainly two functions:

• uttr.ib which generates attributes sensitive to units.
• uttr.array_accessor which allows access to attributes linked to units, and transform them into numpy arrays.

Installing

• From PyPI

$ pip install uttrs

• Simply clone and from within the repo

$ pip install -e .

Quick Start

The following piece of code is an example prototype of a Class representing a Galaxy. The Galaxy contains:

• three arrays (x, y, z) with particle positions, measured in kiloparsecs (u.kpc).
• three arrays (vx, vy, vz) for the particle velocities, measured in Km/s (u.kms/u.s).
• an array (m) of particle masses, expressed in solar masses (u.M_sun).
• a free text for note taking in notes.

In every case we would like to access to position, velocity and mass of the particles, with and without units (as np.ndarray). Suggested units in the information of the attributes behave like this:

• If the user makes the class instance without unit specification then default assumed unit is used.
• If, otherwise, another unit is used as input, it is validated the feasibility of the conversion to default unit.

import attr
import uttr

import astropy.units as u

@attr.s
class Galaxy:
    x = uttr.ib(unit=u.kpc)
    y = uttr.ib(unit=u.kpc)
    z = uttr.ib(unit=u.kpc)

    vx = uttr.ib(unit=u.km/u.s)
    vy = uttr.ib(unit=u.km/u.s)
    vz = uttr.ib(unit=u.km/u.s)

    m = uttr.ib(unit=u.M_sun)

    notes = attr.ib(validator=attr.validators.instance_of(str))

    arr_ = uttr.array_accessor()

Creating a galaxy

>>> import numpy as np
>>> import astropy.units as u

# Creating the particle arrays
>>> x = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)
>>> y = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)
>>> z = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)
>>> vx = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)
>>> vy = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)
>>> vz = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)
>>> m = np.random.randint(1000, 10_000, size=5) + np.random.rand(5)

>>> gal = Galaxy(
...     x = x * u.kpc,  # kpc is the suggested unit
...     y = y * u.mpc,  # mpc is equivalent to kpc
...     z = z,  # we assume is the suggested kpc unit
...     vx = vx * (u.km/u.s), # the suggested unit
...     vy = vy * (u.km/u.s), # the suggested unit
...     vz = vz, # the suggested unit
...     m = m * u.M_sun, # the suggested unit
...     notes="a random galaxy made with random numbers")

>>> gal
Galaxy(
    x=<Quantity [5632.35740606, 1363.36235923, 3037.46794044, 2785.45299727, 2515.35793673] kpc>,
    y=<Quantity [4457.3573917 , 2873.54575512, 7979.68745148, 5930.55394614, 5903.63598164] mpc>,
    z=<Quantity [6122.35929872, 3740.22821927, 6859.42245056, 7119.8256744 , 3632.74980958] kpc>,
    vx=<Quantity [7141.40469733, 5713.29552487, 5000.535142  , 9366.36402447, 2967.2546077 ] km / s>,
    vy=<Quantity [8514.83018331, 1362.13309457, 1136.30959053, 1985.49551226, 3286.69029298] km / s>,
    vz=<Quantity [6218.56279077, 2015.04638043, 9919.99579782, 1278.94359767, 7228.21626876] km / s>,
    m=<Quantity [5640.62516958, 4070.66620947, 6106.583697  , 4063.39917315, 3028.85393523] solMass>,
    notes='a random galaxy made with random numbers')

# we can access al the attributes in the traditional python way
>>> gal.x
<Quantity [5632.35740606, 1363.36235923, 3037.46794044, 2785.45299727, 2515.35793673] kpc>

>>> gal.vz  # z is now a km/s
<Quantity [6218.56279077, 2015.04638043, 9919.99579782, 1278.94359767, 7228.21626876] km / s>

# We stored y as mpc
>>> gal.y
<Quantity [8093.44916403, 2198.55398718, 5464.79397835, 1860.72260272, 3636.64010118] mpc>

Simple interaction with numpy.ndarray

We can access all the same attributes declared with uttr.ib but coerced to the default unit as numpy array.

>>> gal.arr_.y
array([0.00809345, 0.00219855, 0.00546479, 0.00186072, 0.00363664])

The above code is equivalent to

>>> np.asarray(gal.y.to(u.kpc))
array([0.00809345, 0.00219855, 0.00546479, 0.00186072, 0.00363664])

Equivalent units errors

If we change the unit to something not equivalent to the default unit declares in uttr.ib an exception is raised.

Lets fot example define x as a kilogram (u.kg)

>>> gal = Galaxy(
...     x = x * u.kg,  # kg is not equivalent to kpc
...     y = y,
...     z = z,
...     vx = vx,
...     vy = vy,
...     vz = vz,
...     m = m,
...     notes="a random galaxy made with random numbers")

ValueError: Unit of attribute 'x' must be equivalent to 'kpc'.Found 'kg'.

References

Astropy

Price-Whelan, Adrian M., et al. "The Astropy project: Building an open-science project and status of the v2. 0 core package." The Astronomical Journal 156.3 (2018): 123.