Metadata-Version: 2.5
Name: unitx
Version: 0.6.1
Summary: A modern, intuitive Python library for units, quantities, and dimensional analysis.
Project-URL: Homepage, https://github.com/DaitTHU/unitx
Project-URL: Issues, https://github.com/DaitTHU/unitx/issues
Author: Dait
License-Expression: MIT
License-File: LICENSE
Classifier: Programming Language :: Python :: 3
Classifier: Programming Language :: Python :: 3.12
Classifier: Programming Language :: Python :: 3.13
Classifier: Programming Language :: Python :: 3.14
Classifier: Programming Language :: Python :: 3.15
Classifier: Topic :: Scientific/Engineering :: Physics
Requires-Python: >=3.12
Provides-Extra: test
Requires-Dist: pyright>=1.1.414; extra == 'test'
Requires-Dist: pytest>=8; extra == 'test'
Requires-Dist: ruff>=0.8; extra == 'test'
Description-Content-Type: text/markdown

# unitx

Write Python formulas with ready-to-use units and physical constants. unitx
handles scalar quantities, unit conversion, and dimensional analysis, with
exact rational unit scales and exponents.

unitx is in early development. Public APIs may change during the 0.x series.

## Installation

Requires **Python 3.12 or later**, with no mandatory runtime dependencies.

Install a published release:

```sh
python -m pip install unitx
```

To use the current development version, run this from the repository root:

```sh
python -m pip install -e .
```

This README describes the current source tree, including unreleased changes.
For a published release, consult the README at its matching Git tag.

## Quick start

Start with the two namespaces in `unitx.si`: lowercase `si` provides units,
and uppercase `SI` provides physical constants. Their members are ready to use
in ordinary Python formulas:

```pycon
>>> from unitx.si import SI, si
>>> distance = 3 * si.m
>>> elapsed = 2 * si.s
>>> speed = distance / elapsed
>>> print(speed)
1.5 m/s
>>> print(speed.to(si.cm / si.s))
150.0 cm/s
>>> print(SI.c)
299792458 m/s

```

Multiplying a scalar by a unit constructs a quantity. Divide quantities to
compute rates, multiply them to combine physical quantities, and call `.to()`
with the unit you want. A quantity's `.value` and `.unit` expose its magnitude
and unit separately.

## Units and constants with SI

Use the same import for both namespaces:

```python
from unitx.si import SI, si
```

| Namespace | Members | Examples |
| --- | --- | --- |
| `si` | Units (`Unit`) | `si.m`, `si.ns`, `si.kg`, `si.N`, `si.J`, `si.MeV` |
| `SI` | Physical constants (`Quantity`) | `SI.c`, `SI.h`, `SI.hbar`, `SI.e`, `SI.kB`, `SI.me` |

Common prefixed units and units such as hours, litres, electronvolts, and
astronomical units are included. Units and constants can be combined directly:

```pycon
>>> rest_energy = (SI.me * SI.c**2).to(si.MeV)
>>> round(float(rest_energy.value), 6)
0.510999
>>> (2 * si.h).to(si.s).value
7200
>>> (1 * si.us).to(si.ns).value
1000

```

Both namespaces are read-only and do not need to be instantiated. `si` exposes
a selection of convenient attributes; other registered prefix combinations
remain available through `Unit`, for example `Unit('Tm')`. Importing unitx
initializes the predefined unit catalogue. Defining a custom unit registers its
text spellings without adding an attribute to `si`.

SI defining constants retain their exact decimal values. Measured constants
are stored nominal values; measurement uncertainties are not propagated.
Derived constants involving numerical approximations, such as `math.pi`, are
evaluated numerically.

## Constructing units and quantities

For unit expressions and explicit construction, import the classes:

```pycon
>>> from unitx.factor import Factor
>>> from unitx.quantity import Quantity
>>> from unitx.unit import Unit
>>> Quantity(50, 'cm') == 50 * si.cm
True
>>> Unit('astronomical unit') == si.au
True

```

`Quantity(value, unit)` accepts a unit expression or an existing `Unit` object.
`value * unit` constructs a quantity, and `value / unit` constructs a quantity
with the reciprocal unit. Construction preserves the original magnitude and
its type.

Multiplication is symmetric: `unit * value` and `value * unit` both construct
`Quantity` objects and preserve the magnitude's type. Dividing a unit by an
`int`, `Fraction`, or finite `Decimal` constructs a quantity with an exact
`Fraction` reciprocal, so `degree / 60` loses no precision. Float divisors use
native floating-point division without Factor's denominator limit. Booleans
are not accepted as right-hand numeric operands. A `Factor` or
`SymbolicConstant` on either side of a unit instead produces a `ScaledUnit`.

```pycon
>>> metre = Unit('m')
>>> metre * 2 == 2 * metre
True
>>> (metre * 2).value
2
>>> double_metre = metre * Factor(2)
>>> print(double_metre)
2 m
>>> (3 * double_metre).to('m').value
6
>>> arcmin = si.deg / 60
>>> arcmin.value
Fraction(1, 60)
>>> arcmin.to(si.arcmin).value
Fraction(1, 1)

```

Multiplying a `ScaledUnit` by an ordinary number also constructs a quantity,
keeping the exact scale in its unit and preserving the supplied magnitude.
Combining a Unit with a Quantity continues to return a Quantity.

## Conversion and arithmetic

Use `.to()` to convert between units with the same physical dimensions.
Addition and subtraction convert the right operand to the left operand's unit:

```pycon
>>> length = Quantity(1, 'm')
>>> print(length + Quantity(50, 'cm'))
3/2 m
>>> length.to('cm').value
100
>>> Quantity(1, 'cm').to('m').value
Fraction(1, 100)

```

Multiplication and division combine units. Powers apply to both the magnitude
and the unit. Multiplication or division by a `Unit` alone preserves the
magnitude unchanged.

Conversion, addition, subtraction, and ordering across incompatible dimensions
raise `unitx.exceptions.DimensionError`. Equality across incompatible dimensions
returns `False`.

For repeated conversions, reuse a target `Unit` object to avoid parsing the
expression on every call.

## Unit expressions

Expressions support registered symbols, singular English names, SI prefixes,
multiplication, division, parentheses, and rational powers:

```pycon
>>> Unit('kg m/s2') == Unit('kg*m/s**2')
True
>>> Unit('m^(1/2)') ** 2 == Unit('m')
True
>>> Unit('micrometre') == Unit('um')
True
>>> Unit('ms') == Unit('m s')
False

```

- Multiplication can use `*` or whitespace. Adjacent letters form one unit
  token: `ms` is a millisecond, while `m s` is metre times second.
- Powers can use adjacent numbers, `^`, or `**`. Exponents written as ratios
  require parentheses, as in `m^(1/2)`; decimal exponents such as `m^0.5` are exact.
- Multiplication and division associate left to right. Use `m/(s A)` to put
  both `s` and `A` in the denominator; `m/s A` means `(m/s)*A`.
- Unit symbols and names are case-sensitive. `u`, `µ`, and `μ` are accepted
  micro prefixes. Use lowercase `k` for kilo; `K` denotes kelvin.
- A registered multiword name is recognized before implicit multiplication
  when it occupies the entire input. Whitespace between its words is treated
  as a single space. Inside products, parentheses, reciprocals, and powers,
  use its symbol or combine `Unit` objects instead.

The unit table contains `s`, `m`, `g`, `A`, `K`, `mol`, and `cd`, plus the
dimensionless identity. Importing unitx also initializes the common units in
`unitx.si`, including named derived units such as `N`. Mass scales are referenced
to kilograms: `g` has factor `1/1000`, and `kg` has factor `1`.

## Defining units

Call `.define()` on a `Unit`, `ScaledUnit`, or positive real `Quantity` to
register a new unit and return it:

```pycon
>>> newton = Unit('kg*m/s2').define('demoN', 'demo newton')
>>> minute = (60 * Unit('s')).define('demoMin', 'demo minute', prefixable=False)
>>> Quantity(2, minute).to('s').value
120
>>> from unitx.factor import PI
>>> degree = ((PI / 180) * Unit()).define('demoDeg', name='demo degree', prefixable=False)
>>> degree.factor == PI / 180
True
>>> Quantity(1, 'kN').to(newton).value
1000

```

Multiplying or dividing a unit by a `Factor` or `SymbolicConstant` creates a
`ScaledUnit`, which preserves an exact additional
scale through unit arithmetic. Its `scale`
is relative to its formal unit product; its `factor` is the total scale to the
coherent SI unit. An ordinary `Unit` has an implicit additional scale of one;
only `ScaledUnit` stores that scale. Unit multiplication, division, and powers
involving a `ScaledUnit` keep that type even when the scale cancels to one.
A scale of one compares equal to the corresponding `Unit` and has the same
hash. Calling `.define()` returns an ordinary `Unit` with its own formal
identity, sharing the definition's dimension and exact SI factor.

`ScaledUnit` supports shallow copying, deep copying, and pickling while
preserving its exact scale and formal units. Restoring custom units requires
their definitions to be registered in the receiving process.

Definitions affect the current process and leave the source object unchanged.
The symbol is positional-only. The primary `name` accepts positional or keyword
input. Additional name aliases are optional positional arguments after `name`,
such as `Unit('m').define('span', 'spanunit', 'spanlength', 'spanmeasure')`.
Pass the primary name positionally when supplying name aliases; omitting the
aliases gives an empty tuple. `symbol_aliases` accepts a string or tuple of
strings; it and `prefixable` must be passed by keyword.
Symbols and symbol aliases must each be a single printable unit token.
Names and name aliases may contain multiple such tokens separated by single
ASCII spaces, without leading or trailing spaces. Decimal digits and parser
operators are not allowed in any token. The primary symbol and `name` are
required and must be nonempty; empty aliases are ignored.

```pycon
>>> span = (2 * si.m).define('span', 'survey span', 'survey distance')
>>> Unit('survey span') == span
True
>>> Unit('kilosurvey distance') == Unit('kspan')
True
>>> Unit('survey span') / si.s == Unit('span / s')
True

```

Multiword names are recognized only as complete inputs. For example,
`Unit('astronomical unit / arcsec')` does not recognize `astronomical unit`
as a factor; use one of the two compound forms above instead.

SI prefixes are enabled by default; set `prefixable=False` to disable them.
Prefix names attach directly to the first word of a multiword name, as in
`kiloastronomical unit`; a separate `kilo astronomical unit` is not accepted.
Registration raises `UnitRegistryError` if a new spelling, including a generated
prefixed form, already resolves to a unit or conflicts with another spelling
in the same definition. A multiword spelling must not replace an existing
implicit product such as `metre second`. Validation finishes before the
registry changes.

Quantity definitions require positive finite `int`, `Fraction`, `Decimal`, or
`float` magnitudes. Prefer `Fraction` or `Decimal` for exact scales. Floats use
Factor's denominator limit and can warn or round to zero and fail, for example
with `1e-10`. Defining a unit does not evaluate symbolic scales numerically.

## Units, dimensions, and equality

A `Unit` retains its formal factors. A `Quantity` compares physical values
across compatible units:

```pycon
>>> Unit('m') == Unit('cm')
False
>>> Quantity(1, 'm') == Quantity(100, 'cm')
True
>>> len({Quantity(1, 'm'), Quantity(100, 'cm')})
1
>>> from unitx.dimension import Dimension
>>> speed.dimension == Dimension(L=1, T=-1)
True

```

Equal quantities have equal hashes when their magnitudes are hashable. Different
formal unit expressions can have the same physical dimension and scale without
being equal as `Unit` objects.

An expression can be dimensionless and still carry a scale. Plain numbers added
to or subtracted from dimensionless quantities represent unscaled values:

```pycon
>>> scaled = Quantity(1, 'km/m')
>>> scaled.is_dimensionless()
True
>>> scaled == 1000
True
>>> (scaled + 1).to('').value
Fraction(1001, 1)

```

## Numerical behavior

Exact unit algebra and numerical magnitude evaluation have different rules:

- Rational unit scales and exponents remain exact. Prefer `Fraction` or
  `Decimal` for exact exponents; float exponents may be approximated with an
  `InexactFloatWarning`.
- Conversion and arithmetic can change the magnitude's type. Finite `Decimal`
  operands are converted exactly to `Fraction`, without Decimal context
  rounding.
- Other magnitudes use native numerical arithmetic. In particular, integer
  division produces a float, and nonintegral magnitude powers can round or
  produce complex values.
- Equality is exact, without a tolerance. Finite floats are compared as their
  stored binary rational values. Floating-point conversions and irrational
  powers may round; compare their values approximately in a common unit when
  appropriate.

```pycon
>>> from decimal import Decimal
>>> from fractions import Fraction
>>> Quantity(Decimal('0.1'), 'm').to('cm').value
10
>>> (Quantity(Fraction(1), 'm') / Quantity(3, 's')).value
Fraction(1, 3)
>>> Quantity(0.1, '') == Quantity(Fraction(1, 10), '')
False

```

The built-in integer factorization backend is bounded. Unresolved factors emit
`IncompleteFactorWarning` and can limit simplification and comparisons. SymPy
is an optional, more capable factorization backend:

```sh
python -m pip install sympy
```

## Current scope

- **NumPy scalars, arrays, and NumPy operations are not supported yet. NumPy
  integration is planned.** Structural compatibility with a magnitude protocol
  does not imply NumPy support.
- Custom magnitudes must support scalar arithmetic, return a Python `bool`
  from equality, and defer raw operations with `Unit` operands to its reflected
  operators.
- Scalar multiplication and division of quantities currently accept `int`,
  `float`, `Fraction`, and `Decimal`. Complex magnitudes are supported, including
  results of fractional powers; ordering follows the magnitude's native rules.
- Unit conversion is multiplicative. Offset temperature scales such as Celsius
  and Fahrenheit are not supported.

## Building blocks

| Class | Import module | Purpose |
| --- | --- | --- |
| `si` / `SI` | `unitx.si` | Ready-to-use units and physical constants |
| `Quantity` | `unitx.quantity` | Scalar values paired with units, conversion, and arithmetic |
| `Unit` | `unitx.unit` | Compound units, scaling factors, and physical dimensions |
| `ScaledUnit` | `unitx.unit` | Formal unit products with an additional exact scale |
| `Dimension` | `unitx.dimension` | Seven physical dimensions with rational exponents |
| `SingleUnit` | `unitx.singleunit` | One registered unit with an optional prefix |
| `Factor` | `unitx.factor` | Positive scaling expressions and magnitude scaling |
| `UnitParser` | `unitx.unitparser` | Parsing unit expressions into formal products |
| `Monomial` | `unitx.monomial` | Immutable formal products with rational exponents |

The package includes inline type annotations and a `py.typed` marker. Construction
and operations with `Unit` preserve the magnitude type in type hints; conversion
and numerical arithmetic use result unions where the concrete type depends on
runtime values or units. Modules whose names start with `_` are internal.

## Upgrading from 0.3.0

Version 0.4.0 replaced the implementation previously published on PyPI as 0.3.0.
It introduced incompatible changes:

- Python 3.12 or later is required; Python 3.11 is no longer supported.
- The former `unitx.utils` namespace was removed. Classes can be imported from
  their modules, as shown above; the current source tree also exports `Unit`,
  `Quantity`, and `Dimension` at the package root.
- `Unit` no longer defines `len()` or special truth-value behavior. Use
  `unit == Unit('')` to check the formal identity, or `unit.is_dimensionless()`
  to check physical dimensions.
- Conversion and arithmetic can produce different magnitude types, especially
  for Decimal inputs. Review the [numerical behavior](#numerical-behavior)
  before relying on a result's concrete type or approximate equality.

## Development

Install the development version and test dependencies:

```sh
python -m pip install -e ".[test]"
python -m pytest -q
python -m ruff check .
python -m ruff format --check .
```

The pytest suite includes doctests and Pyright checks for the typed API. CI runs
the suite with both the built-in and SymPy factorization backends.

## Releases

The [release workflow](.github/workflows/release.yml) validates the source,
builds a wheel and source distribution, checks their metadata, and tests the
installed wheel. Manual workflow runs store the distributions without uploading
them to PyPI.

Publishing a GitHub release runs the same checks and uploads the distributions
to PyPI. The release tag must match the project version, for example `v0.4.0`
for version `0.4.0`. Configure a PyPI Trusted Publisher for the repository,
workflow `release.yml`, and GitHub environment `pypi` before publishing.

See [CHANGELOG.md](CHANGELOG.md) for release history. Licensed under the
[MIT License](LICENSE).
