Composing and defining units

Units can be composed together using the regular Python numeric operators. For example:

>>> from astropy import units as u
>>> fluxunit = u.erg / (u.cm ** 2 * u.s)
>>> fluxunit
Unit("erg / (cm2 s)")

Users are free to define new units, either fundamental or compound using the def_unit function. For example:

>>> bakers_fortnight = u.def_unit('bakers_fortnight', 13 * u.day)

The addition of a string gives the new unit a name that will show up when the unit is printed.

Creating a new fundamental unit is simple:

>>> titter = u.def_unit('titter')
>>> chuckle = u.def_unit('chuckle', 5 * titter)
>>> laugh = u.def_unit('laugh', 4 * chuckle)
>>> guffaw = u.def_unit('guffaw', 3 * laugh)
>>> rofl = u.def_unit('rofl', 4 * guffaw)
>>> death_by_laughing = u.def_unit('death_by_laughing', 10 * rofl)
>>> rofl.to(titter, 1)
240

Reducing a unit to its irreducible parts

A unit can be decomposed into its irreducible parts using the decompose method:

>>> u.Ry
Unit("Ry")
>>> u.Ry.decompose()
Unit("2.18e-18 m2 kg / (s2)")

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