SciPy – Constants

Scipy stands for Scientific Python and in any Scientific/Mathematical calculation, we often need universal constants to carry out tasks, one famous example is calculating the Area of a circle = ‘pi*r*r’ where PI = 3.14… or a more complicated one like finding force_gravity = G*M*m ⁄ (distance)² where G = gravitational constant. In all such scenarios, it would be very handy if we have reference material to look up these constants and incorporate them into our calculation with ease.

Scipy-Constants is a sub-module inside the Scipy library that does this for us. It contains an exhaustive list of universal mathematical constants, Physical constants, and units. which can be looked up with just 1 line of code.

Accessing Constants

Just type the name of the constant in place of XXXX in ‘scipy.constants.XXXX‘ format to access its value. Below listed are a few most important constants using scipy.constant module down below. The list is not exhaustive, but it gives a good idea of how to access constants.  

Python3

# import module
import scipy

# Just type the name of the constant in
# scipy.constant.XXXX format to access its value.
print("sciPy - pi:", scipy.constants.pi)
print("Golden ratio:", scipy.constants.golden_ratio)
print("Speed of light in vacuum:", scipy.constants.c)
print("Gravitational Constant:", scipy.constants.G)
print("Molar Gas Constant:", scipy.constants.R)
print("Boltzman Constant:", scipy.constants.k)
print("Proton mass Constant:", scipy.constants.proton_mass)

Output:

Finding Constants

We can use an inbuilt method to find the constants relevant to our use case. Constants are stored using a dictionary data structure, and we can use the scipy. constants.find() API to find all relevant constants from the dict and use them accordingly. 

The code below demonstrates using scipy. constants.find() API. The below code prints all constants which contain the ‘electron’ word in it, and we can filter out the one which is required. 

Python3

import scipy


# find method looks up in the dictorary and
# finds out all the constants containing
# 'electron' word in it and returns a list
# of constants.
res = scipy.constants.find("electron")
print(res, end='\n')

Output:

Not just the magnitude of a constant we can also access the unit and degree of uncertainty associated with the magnitude of any physical_constants stored in scipy.constants module, using the format

physical_constants[name] = (value, unit, uncertainty).

Python3

import scipy


# This returns a tuple (value, unit, uncertainty)
# associated with the physical constant
print(scipy.constants.physical_constants['alpha particle mass'])

Output: 

(6.6446573357e-27, 'kg', 2e-36)

Example:

Python3

import scipy

# Area of a circle using
# scipy.constants.pi
def Area_of_Circle(r):
    return scipy.constants.pi * r * r

# Calculates the gravational for
def force_gravity(M, m, dist):
    return (scipy.constants.G*M*m) / (dist**2)


print(f'Area of Circle: {Area_of_Circle(5)}')
print(f'Gravitational force: {force_gravity(10,5,1)}')

Output:

Apart from the above variables, scipy.constants also contain more physical constants, and below is a list of all methods available in scipy.constants module with an explanation.

Below are the most commonly used constants available in SciPy module:

Constants	Description
pi	Mathematical pi value
golden	Mathematicalgolden ratio
c	Speed of light in vacuum
speed_of_light	Speed of light in vacuum
G	Standard acceleration of gravity
G	Newton Constant of gravitation
E	Elementary charge
R	Molar gas constant
Alpha	Fine-structure constant
N_A	Avogadro constant
K	Boltzmann constant
Sigma	Stefan-Boltzmann constant σ
m_e	Electron mass
m_p	Proton mass
m_n	Neutron Mass
H	Plank Constant
Plank constant	Plank constant h

Below are the unit constants available in the SciPy module:

• Mass:

Unit	Description
Gram	One gram in Kilogram.
Grain	One grain in Kilogram.
Pound	One Pound in Kilogram.
Ounce	One Ounce in Kilogram.
automic_mass	Atomics mass constant in Kilogram.

• Time:

Unit	Description
Minute	One minute in seconds.
Hour	One hour in seconds.
Day	One day in seconds.
Year	One year in seconds.

• Length:

Units	Description
Inch	One inch in meters.
Foot	One foot in meters.
Yard	One yard in meters.
Pt	One point in meters.
Micron	One Micron in meters.

• Pressure:

Units	Description
Atm	The standard atmosphere in pascals.
Atmosphere	The standard atmosphere in pascals.
Bar	One bar in Pascals.
Torr	One torr(mmHg) in pascals.

• Area:

Units	Description
Hectare	One hectare in square meters.
Acre	One acre in square meters.

• Speed:

Units	Description
Kmh	Kilometer per hour in meter per second.
Mph	Miles per hour in meter per second.
Mach	One Match in meter per second.