UnitPy (Unit Python)

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UnitPy is a Python package for defining, converting, and working with units.

The goal of the package is to be simple, straightforward, and performant.

This package directly implements NIST (National Institute of Standards and Technology) official unit definitions.

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Installation

Pip installable package:

pip install unitpy

pypi: unitpy

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Requirements / Dependencies

Python 3.8 and up

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Basic Usage

Defining Unit

from unitpy import U, Q, Unit, Quantity
# U = Unit

u = Unit("kilometer")
u = U("kilometer")
u = U("km")
u = U.kilometer
u = U.km

u = U("kilometer/hour")
u = U("km/h")
u = U.kilometer / U.hour
u = U.km / U.h

# properties
print(u.dimensionality)  # [length] / [time]
print(u.dimensionless)   # False
print(u.base_unit)       # meter / second

Defining Quantity

** Quantity = Value + Unit **

from unitpy import U, Q , Unit, Quantity
# Q = Quantity

q = 1 * U("kilometer/hour") 
q = 1 * (U.kilometer / U.hour)
q = Quantity("1 km/h")
q = Q("1 kilometer per hour")
q = Q("1*kilometer/hour")


# properties
print(q.unit)            # kilometer / hour
print(q.dimensionality)  # [length] / [time]
print(q.dimensionless)   # False
print(q.base_unit)       # meter / second

Unit Conversion

from unitpy import U, Q , Unit, Quantity
# Q = Quantity

q = 1 * U("km/h") 
q2 = q.to("mile per hour")
print(q2)  # 0.6213711922 mile / hour

Mathematical operation

from unitpy import U, Q 

q = 1 * U("km/h") 
q2 = 2.2 * U("mile per hour")
print(q2 + q)                 # 2.8213711923 mile / hour
print(q2 - q)                 # 1.5786288077 mile / hour
print(q2 * q)                 # 2.2 kilometer mile / hour**2
print(q2 / q)                 # 2.2 mile / kilometer
print((q2 / q).dimensionless) # True

Other supported functions:

• sum
• max
• min

Temperature

Abbreviations:

• fahrenheits: degF
• celsius: degC
• kelvin: degK, K
• rankine: degR

from unitpy import U, Q

q = 300 * U("K")
q2 = 200 * U("K")

print(q + q2)        # 500.0 kelvin
print(q.to("degC"))  # 26.85 Celsius
print(q.to("degF"))  # 830.6344444444 Fahrenheit
print(q.to("degR"))  # 166.6666666667 Rankine

Temperature units are non-multiplicative units. They are expressed with respect to a reference point (offset).

degC = 5/9 * (degF - 32)

Default behavior is absolute units.

For relative units use dedicated functions add_rel() or sub_rel().

from unitpy import U, Q

q = 10 * U("degC")
q2 = 5 * U("degC")

# absolute
print(q.to("K"))         # 283.15 kelvin
print(q + q2)            # 288.15 Celsius 
print((q + q2).to("K"))  # 561.3 kelvin
print(q - q2)            # -268.15 Celsius
print((q - q2).to("K"))  # 5.0 kelvin

# relative
print(q.add_rel(q2))      # 15 Celsius
print(q.sub_rel(q2))      # 5 Celsius
print(abs(-10 * U.degC))  # 10 Celsius

Time

from datetime import timedelta
from unitpy import U

a = 1.234 * U.min
print(a)              # 1.234 minute
b = a.to_timedelta()
print(b)              # 0:01:14.040000
print(type(b))        # <class 'datetime.timedelta'>

string formatting

from unitpy import U

a = 1.23432453 * U.min
print(a)                # 1.23432453 minute
print(f"{a:.2f}")       # 1.23 minute
b = 1_000_000 * U.cm
print(b)                # 1000000 centimeter
print(format(b, ","))   # 1,000,000 centimeter
c = 123 * U.inch
print(c)                # 123 inch
print(f"{c:5}")         #   123 inch  (leading spaces)
print(f"{c:05}")        # 00123 inch  (leading zeros)

configuration with .env

To configure the string outputs with environment file (.env):

1. install python-dotenv. The code uses this to load variables from the .env file

pip install python-dotenv

2. copy the .env file from this repo into the top level of your repo and edit to your liking

It should now load the environmental variables when you run the code to format it to your liking without any additional code needed.

Numpy Support

Numpy

import numpy as np

from unitpy import Unit, Quantity

# numpy + int
a = np.linspace(0, 4, 5) * Unit.m
b = 1 * Unit.ft
c = a+b
print(a+b)                           # [0.3048 1.3048 2.3048 3.3048 4.3048] meter
print(a-b)                           # [-0.3048  0.6952  1.6952  2.6952  3.6952] meter
a += b
print(a)                             # [0.3048 1.3048 2.3048 3.3048 4.3048] meter

# numpy + numpy
a = np.linspace(0, 4, 5) * Unit.m
b = np.linspace(0, 4, 5) * Unit.ft
print(a+b)                           # [0.     1.3048 2.6096 3.9144 5.2192] meter
print(a-b)                           # [0.     0.6952 1.3904 2.0856 2.7808] meter
a += b
print(a)                             # [0.     1.3048 2.6096 3.9144 5.2192] meter

# numpy * int
a = np.linspace(0, 4, 5) * Unit.m
b = 1.2 * Unit.s
print(a*b)                            # [0.  1.2 2.4 3.6 4.8] meter second
print(a/b)                            # [0.  0.83333333 1.66666667 2.5 3.33333333] meter/second
a *= b
print(a)                              # [0.  1.2 2.4 3.6 4.8] meter second

# numpy * numpy
a = np.linspace(0, 4, 5) * Unit.m
b = np.linspace(0, 4, 5) * Unit.s
print(a*b)                              # [ 0.  1.  4.  9. 16.] meter second
print(a/b)                              # [nan  1.  1.  1.  1.] meter/second
a *= b
print(a)                                # [ 0.  1.  4.  9. 16.] meter second


# numpy functions
a = np.linspace(-2, 4, 5) * Unit.m
print(np.sum(a))                       # 5 meter
print(np.max(a))                       # 4 meter
print(np.abs(a))                       # [2.  0.5 1.  2.5 4. ] meter
print(np.linspace(1*Unit.mm, 2*Unit.ft, 4))  # [  1.         203.86666667 406.73333333 609.6       ] millimeter

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Notes

• this package utilizes the American spellings "meter," "liter," and "ton"
• supports pickling