escope.units module

class escope.units.Units(value: float | ndarray | str, unit: str | None = None)

Bases: object

Class for unit conversion

Examples

Units(“4 lbs”).asunits(“kg”) → 1.814

Units(“3 V / 200 mA”).asunits(“Ohm”) → 15.0

Units(“psi”).definition() → “6894.7573 kg m^-1 s^-2”

The full syntax for unit specification is:

BASEUNIT: m | s | g | A | mol
PREFIX: m | u | n | p | f | k | M | G | T
ALTUNIT: meter | meters | second | seconds | sec | secs | gram | grams | gm | amp | amps | ampere | amperes | Amp | Ampere | Amperes
ALTPREFIX: milli | micro | μ | nano | pico | femto | kilo | mega | Mega | giga | Giga | tera | Tera
DERIVEDUNIT: in | inch | Hz | Hertz | hertz | cyc | cycles | V | volt | Volt | volts | Volts | N | newton | Newton | newtons | Newtons | Pa | pascal | bar | atm | torr | J | joule | joules | Joule | Joules | barn | Ohm | Ohms | ohm | ohms | mho | Mho
UNIT: (PREFIX | ALTPREFIX)? (BASEUNIT | ALTUNIT | DERIVEDUNIT)
DIGITS: [0-9]
INTEGER: (‘-’ | ‘+’)? DIGIT+
NUMBER: (‘-’ | ‘+’)? DIGIT* (‘.’ DIGIT*)? (‘e’ (‘+’ | ‘-’) DIGIT*)?
POWFRAC: INTEGER (‘|’ INTEGER)?
POWERED: UNIT (‘^’ POWFRAC)?
FACTOR: POWERED | NUMBER
MULTI: FACTOR (’ ‘ MULTI)?
FRACTION: MULTI (‘/’ MULTI)?

Thus, the following would be understood:

‘kg m / s^2’
That’s a newton

‘J / Hz^1|2’
Joules per root-Hertz

Multiplication is implicit; do not attempt to write ‘*’.

Fractions in exponents must be written with ‘|’ rather than ‘/’, as ‘|’ binds more tightly than ‘^’.

Division marked by ‘/’ binds most loosely, e.g,

‘kg / m s’ – kilogram per meter per second

Syntax checking is not overly rigorous. Some invalid expressions may return meaningless values without a reported error.

definition(withoutvalue=False)

Definition of stored value in SI units

withoutvalue: If given as True, only the base unit is returned, not the value-with-units

The definition of the stored unit in terms of SI base units.

Units(“2 lb”).definition() → “0.907 kg”

Units(“psi”).definition(True) → “kg m^-1 s^-2”

asunits(newunit: str, warn=False) → float | ndarray

Convert to different units

The conversion result. The shape and data type of the result will match the original value passed into the Units constructor.

An exception is raised if the units are incompatible.

Optional argument WARN, if True, turns that into a warning.

See the class documentation for unit syntax and note that addition or subtraction is not supported.