Custom Modules

4.12. Custom Modules#

There are lots of Python modules that exist for us to use. E.g. math, random, time and datetime modules.

But if we want to write our own custom functions we can actually write our own modules! We just need to create a Python file:

module.py

where we write all of our functions. We can then import this as we would with our usual modules.

import module

To use a function in our module, we use:

module.function()
Code Challenge: Rectangle Properties

Write a module called rectangle that can be used to calculate properties of rectangles. You should be able to import functions from you module into your main script. Your module should contain the following 3 functions.

Area specification (written in rectangle.py)

Formula for the area of a rectangle

\(\text{area} = \text{width} \times \text{height}\)

  • name: area

  • parameters: width (int or float), height (int or float)

  • return: the area of the rectangle (int or float)

Perimeter specification (written in rectangle.py)

Formula for the perimeter of a rectangle

\(\text{perimeter} = 2\times\text{width} + 2 \times \text{height}\)

  • name: perimeter

  • parameters: width (int or float), height (int or float)

  • return: the perimeter of the rectangle (int or float)

Diagonal specification (written in rectangle.py)

Formula for the diagonal of a rectangle

\(\text{diagonal} = \sqrt{\text{width}^2 + \text{height}^2}\)

  • name: perimeter

  • parameters: width (int or float), height (int or float)

  • return: the perimeter of the rectangle (int or float)

Examples (running from main.py)

import rectangle

print(rectangle.area(2, 10))
print(rectangle.perimeter(5, 7))
print(rectangle.diagonal(3, 4))

20
24
5.0
Solution

Solution is locked

Code Challenge: Intergalactic

Write a program that calculates an object’s weight in Newtons on the surface of:

  • Earth, and

  • another planet,

to four decimal places.

Your project must consists of two files:

  1. intergalactic.py - takes care of input/output and running the program

  2. physics.py - holds functions for the calculations

Acceleration specification (written in physics.py)

Formula for acceleration due to gravity on a planet’s surface

\(a = \frac{G m}{r^2}\)

where \(G = 6.67430\times10^{-11}\) is the gravitational constant and \(m`\) and \(r`\) are the mass and radius of the planet respectively.

  • name: acceleration

  • parameters: planet_mass (float expected - kg), planet_radius (float expected - m)

  • return: acceleration due to gravity on the planet’s surface (float)

Weight specification (written in physics.py)

Formula for calculating weight from object’s mass and acceleration

\(w = mg\)

where \(w`\) is the weight of the object in Newtons, \(m`\) is the mass of the object in kg and \(a`\) is the acceleration due to gravity on the planet. By default \(a = 9.80665\) m/s/s.

  • name: weight

  • parameters: object_mass (float expected - kg), planet_acceleration (default=9.80665,``float`` expected - m/s/s)

  • return: object’s weight (float)

In your intergalactic.py file you should write a program that asks the user for an objects mass, planet’s mass and planet’s radius. Your program should then tell the user the weight of the given object on Earth and the weight on the specified planet to 4 decimal places.

Example 1 (running from intergalactic.py)

Object's mass (kg): 100
Other planet's mass (kg): 0.642e24
Other planet's radius (m): 3396000
Weight on Earth (Newtons): 980.6650
Weight on other Planet (Newtons): 371.5398

Example 2 (from intergalactic.py)

Object's mass (kg): 50
Other planet's mass (kg): 1.898e27
Other planet's radius (m): 7.1492e7
Weight on Earth (Newtons): 490.3325
Weight on other Planet (Newtons): 1239.2446

Hint

We can represent very small numbers or very large numbers using scientific notation. eX is used to represented \(\times 10^{X}\). For example 1e-3 is equivalent to \(1 \times 10^{-3}\) and 5e2 is equivalent to \(5\times10^{2}\). Python can automatically convert string representations of these values to floats.

Floats can convert strings with scientific notation.

x = '1e-3'
print(float(x))

y = '5e2'
print(float(y))

0.001
500.0
Solution

Solution is locked