UnitBase¶

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
aliases
Returns the alias (long) names for this unit. bases
Return the bases of the unit. cgs
Returns a copy of the current Unit
instance with CGS units.name
Returns the canonical (short) name associated with this unit. names
Returns all of the names associated with this unit. physical_type
Return the physical type on the unit. powers
Return the powers of the unit. scale
Return the scale of the unit. si
Returns a copy of the current Unit
instance in SI units.Methods Summary
compose
(self[, equivalencies, units, …])Return the simplest possible composite unit(s) that represent the given unit. decompose
(self[, bases])Return a unit object composed of only irreducible units. find_equivalent_units
(self[, equivalencies, …])Return a list of all the units that are the same type as self
.in_units
(self, other[, value, equivalencies])Alias for to
for backward compatibility with pynbody.is_equivalent
(self, other[, equivalencies])Returns True
if this unit is equivalent toother
.is_unity
(self)Returns True
if the unit is unscaled and dimensionless.to
(self, other[, value, equivalencies])Return the converted values in the specified unit. to_string
(self[, format])Output the unit in the given format as a string. to_system
(self, system)Converts this unit into ones belonging to the given system. Attributes Documentation

aliases
¶ Returns the alias (long) names for this unit.

bases
¶ Return the bases of the unit.

name
¶ Returns the canonical (short) name associated with this unit.

names
¶ Returns all of the names associated with this unit.

physical_type
¶ Return the physical type on the unit.
Examples
>>> from astropy import units as u >>> print(u.m.physical_type) length

powers
¶ Return the powers of the unit.

scale
¶ Return the scale of the unit.
Methods Documentation

compose
(self, 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:  equivalencies : list of equivalence pairs, optional
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
. UseNone
to turn off all equivalencies. units : set of units to compose to, 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_depth : int, optional
The maximum recursion depth to use when composing into composite units.
 include_prefix_units : bool, optional
When
True
, include prefixed units in the result. Default isTrue
if a sequence is passed in tounits
,False
otherwise.
Returns:  units : list 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
(self, bases=set())[source]¶ Return a unit object composed of only irreducible units.
Parameters:  bases : sequence 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:  unit : CompositeUnit object
New object containing only irreducible unit objects.

find_equivalent_units
(self, equivalencies=[], units=None, include_prefix_units=False)[source]¶ Return a list of all the units that are the same type as
self
.Parameters:  equivalencies : list of equivalence pairs, optional
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
) units : set of units to search in, 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_units : bool, optional
When
True
, include prefixed units in the result. Default isFalse
.
Returns:

in_units
(self, other, value=1.0, equivalencies=[])[source]¶ Alias for
to
for backward compatibility with pynbody.

is_equivalent
(self, other, equivalencies=[])[source]¶ Returns
True
if this unit is equivalent toother
.Parameters:  other : unit object or string 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.
 equivalencies : list of equivalence pairs, optional
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
. UseNone
to turn off all equivalencies.
Returns:  bool

to
(self, other, value=1.0, equivalencies=[])[source]¶ Return the converted values in the specified unit.
Parameters:  other : unit object or string
The unit to convert to.
 value : scalar int or float, or sequence convertible to array, optional
Value(s) in the current unit to be converted to the specified unit. If not provided, defaults to 1.0
 equivalencies : list of equivalence pairs, optional
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
. UseNone
to turn off all equivalencies.
Returns:  values : scalar or array
Converted value(s). Input value sequences are returned as numpy arrays.
Raises:  UnitsError
If units are inconsistent

to_string
(self, format=<class 'astropy.units.format.generic.Generic'>)[source]¶ Output the unit in the given format as a string.
Parameters:  format :
astropy.units.format.Base
instance or str The name of a format or a formatter object. If not provided, defaults to the generic format.
 format :

to_system
(self, system)[source]¶ Converts this unit into ones belonging to the given system. Since more than one result may be possible, a list is always returned.
Parameters:  system : module
The module that defines the unit system. Commonly used ones include
astropy.units.si
andastropy.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:  units : list of
CompositeUnit
The list is ranked so that units containing only the base units of that system will appear first.
