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UnitBase — Astropy v7.1.0

class astropy.units.UnitBase[source]#

Bases: object

Abstract base class for units.

Most of the arithmetic operations on units are defined in this base class.

Should not be instantiated by users directly.

Attributes Summary

Methods Summary

Attributes Documentation

bases#

The bases of the unit.

cgs#

The unit expressed in terms of CGS units.

physical_type#

Physical type(s) dimensionally compatible with the unit.

Returns:

PhysicalType

A representation of the physical type(s) of a unit.

Examples

>>> from astropy import units as u
>>> u.m.physical_type
PhysicalType('length')
>>> (u.m ** 2 / u.s).physical_type
PhysicalType({'diffusivity', 'kinematic viscosity'})

Physical types can be compared to other physical types (recommended in packages) or to strings.

>>> area = (u.m ** 2).physical_type
>>> area == u.m.physical_type ** 2
True
>>> area == "area"
True

PhysicalType objects can be used for dimensional analysis.

>>> number_density = u.m.physical_type ** -3
>>> velocity = (u.m / u.s).physical_type
>>> number_density * velocity
PhysicalType('particle flux')

powers#

The powers of the bases of the unit.

scale#

The scale of the unit.

si#

The unit expressed in terms of SI units.

Methods Documentation

compose(equivalencies=[], units=None, max_depth=2, include_prefix_units=None)[source]#

Return the simplest possible composite unit(s) that represent the given unit. Since there may be multiple equally simple compositions of the unit, a list of units is always returned.

Parameters:

equivalencieslist of tuple

A list of equivalence pairs to also list. See Equivalencies. This list is in addition to possible global defaults set by, e.g., set_enabled_equivalencies. Use None to turn off all equivalencies.

unitsset of Unit, optional

If not provided, any known units may be used to compose into. Otherwise, units is a dict, module or sequence containing the units to compose into.

max_depthint, optional

The maximum recursion depth to use when composing into composite units.

include_prefix_unitsbool, optional

When True, include prefixed units in the result. Default is True if a sequence is passed in to units, False otherwise.

Returns:

unitslist of CompositeUnit

A list of candidate compositions. These will all be equally simple, but it may not be possible to automatically determine which of the candidates are better.

decompose(bases: Collection[UnitBase] = ()) → UnitBase[source]#

Return a unit object composed of only irreducible units.

Parameters:

basessequence of UnitBase, optional

The bases to decompose into. When not provided, decomposes down to any irreducible units. When provided, the decomposed result will only contain the given units. This will raises a UnitsError if it’s not possible to do so.

Returns:

unitCompositeUnit

New object containing only irreducible unit objects.

find_equivalent_units(equivalencies=[], units=None, include_prefix_units=False)[source]#

Return a list of all the units that are the same type as self.

Parameters:

equivalencieslist of tuple

A list of equivalence pairs to also list. See Equivalencies. Any list given, including an empty one, supersedes global defaults that may be in effect (as set by set_enabled_equivalencies)

unitsset of Unit, optional

If not provided, all defined units will be searched for equivalencies. Otherwise, may be a dict, module or sequence containing the units to search for equivalencies.

include_prefix_unitsbool, optional

When True, include prefixed units in the result. Default is False.

Returns:

unitslist of UnitBase

A list of unit objects that match u. A subclass of list (EquivalentUnitsList) is returned that pretty-prints the list of units when output.

get_converter(other, equivalencies=[])[source]#

Create a function that converts values from this unit to another.

Parameters:

otherastropy:unit-like

The unit to convert to.

equivalencieslist of tuple

A list of equivalence pairs to try if the units are not directly convertible. See Equivalencies. This list is in addition to possible global defaults set by, e.g., set_enabled_equivalencies. Use None to turn off all equivalencies.

Returns:

funccallable()

A callable that takes an array-like argument and returns it converted from units of self to units of other.

Raises:

UnitsError

If the units cannot be converted to each other.

Notes

This method is used internally in Quantity to convert to different units. Note that the function returned takes and returns values, not quantities.

in_units(other, value=1.0, equivalencies=[])[source]#

Deprecated since version 7.0: The in_units function is deprecated and may be removed in a future version. Use to() instead.

Alias for to for backward compatibility with pynbody.

is_equivalent(other, equivalencies=[])[source]#

Check whether this unit is equivalent to other.

Parameters:

otherUnit, str, or tuple

The unit to convert to. If a tuple of units is specified, this method returns true if the unit matches any of those in the tuple.

equivalencieslist of tuple

A list of equivalence pairs to try if the units are not directly convertible. See Equivalencies. This list is in addition to possible global defaults set by, e.g., set_enabled_equivalencies. Use None to turn off all equivalencies.

Returns:

bool

is_unity() → bool[source]#

Check whether the unit is unscaled and dimensionless.

to(other, value=1.0, equivalencies=[])[source]#

Return the converted values in the specified unit.

Parameters:

otherastropy:unit-like

The unit to convert to.

valueint, float, or scalar array_like, optional

Value(s) in the current unit to be converted to the specified unit. If not provided, defaults to 1.0

equivalencieslist of tuple

A list of equivalence pairs to try if the units are not directly convertible. See Equivalencies. This list is in addition to possible global defaults set by, e.g., set_enabled_equivalencies. Use None to turn off all equivalencies.

Returns:

valuesscalar or array

Converted value(s). Input value sequences are returned as numpy arrays.

Raises:

UnitsError

If units are inconsistent

to_string(format: type[Base] | str | None = None, **kwargs) → str[source]#

Output the unit in the given format as a string.

Parameters:

formatastropy.units.format.Base subclass or str or None

The name of a format or a formatter class. If not provided (or None), defaults to the generic format.

**kwargs

Further options forwarded to the formatter. Currently recognized is fraction, which can take the following values:

• False : display unit bases with negative powers as they are;

• ‘inline’ or True : use a single-line fraction;

• ‘multiline’ : use a multiline fraction (available for the ‘latex’, ‘console’ and ‘unicode’ formats only; for others, an ‘inline’ fraction is used).

Raises:

TypeError

If format is of the wrong type.

ValueError

If format or fraction are not recognized.

Examples

>>> import astropy.units as u
>>> kms = u.Unit('km / s')
>>> kms.to_string()  # Generic uses fraction='inline' by default
'km / s'
>>> kms.to_string('latex')  # Latex uses fraction='multiline' by default
'$\\mathrm{\\frac{km}{s}}$'
>>> print(kms.to_string('unicode', fraction=False))
km s⁻¹
>>> print(kms.to_string('unicode', fraction='inline'))
km / s
>>> print(kms.to_string('unicode', fraction='multiline'))
km
──
s

to_system(system)[source]#

Convert this unit into ones belonging to the given system.

Since more than one result may be possible, a list is always returned.

Parameters:

systemmodule

The module that defines the unit system. Commonly used ones include astropy.units.si and astropy.units.cgs.

To use your own module it must contain unit objects and a sequence member named bases containing the base units of the system.

Returns:

unitslist of CompositeUnit

With an attempt to sort simpler units to the start (see examples).

Examples

>>> import astropy.units as u
>>> (u.N / u.m**2).to_system(u.si)  # preference for simpler units
[Unit("Pa"), Unit("N / m2"), Unit("J / m3")]
>>> u.Pa.to_system(u.cgs)
[Unit("10 Ba"), Unit("10 P / s")]
>>> u.Ba.to_system(u.si)
[Unit("0.1 Pa"), Unit("0.1 N / m2"), Unit("0.1 J / m3")]
>>> (u.AU/u.yr).to_system(u.cgs)  # preference for base units
[Unit("474047 cm / s"), Unit("474047 Gal s")]
>>> (u.m / u.s**2).to_system(u.cgs)
[Unit("100 cm / s2"), Unit("100 Gal")]

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