For creating great software products it is key to have a good set of developing practices. In this talk I go over some of the most important patterns and strategies for developing products in Python. The talk was given at Imperial College London in June 2018.

1. Dr. Miguel Fierro
@miguelgfierro
Best practices in coding for
beginners

2. 2
Pursuing Artificial Intelligence
Language
Speech
Search
Machine
Learning
Knowledge Vision

3. 3
Agenda
The why, the what and the how of Python
Development
strategies
Software development principles
What’s next?

4. 4
Agenda
The why, the what and the how of Python
Development
strategies
Software development principles
What’s next?

5. Why Python?
Most popular language
According to PYPL, Python
surpassed Java in 2018 as the most
popular programming language.
The language of AI
It has became the language of AI,
machine learning and deep learning.
Most of the top AI libraries use
python.
Easier
As Python typically involves less
code, it also takes less time to
complete a job. This also means
less money.
Dr. Miguel Fierro - @miguelgfierro

6. 6
The final 2.x version 2.7 release came out in
mid-2010
Python 2.7 will only receive necessary security
updates until 2020
Python 3.5 was released in 2015 and Python
3.6 in 2016.
All recent standard library improvements are
available in Python 3.x by default
Python 2.x Python 3.x
Python 3.x is the present and future
of the language
Dr. Miguel Fierro - @miguelgfierro

7. 7
$ source activate my_env
(my_env) $ pip install –r requirements.txt
bash
Python environments
# file: requirements.txt
Django==1.7.10
markdown2==2.3.0
Pillow==4.2.1
numpy>=1.13.3
opencv>=3.3.0
pyodbc>=4.0.21
requests>=2.18.4
beautifulsoup4>=4.6.0
pandas>=0.22.0
scikit-image>=0.13.1
scikit-learn>=0.19.1
scipy>=0.19.0
matplotlib>=1.5.3
file
Python environments encapsulate development
Dr. Miguel Fierro - @miguelgfierro

8. 8
$ conda create –n my_env –f conda.yaml
$ source activate my_env
(my_env) $
bash
Conda environments
# file: conda.yaml
channels:
- conda-forge
- defaults
dependencies:
- python==3.6
- numpy==1.13.3
- flask==1.0.2
- cherrypy==12.0.1
- ipykernel==4.6.1
- pip:
- pandas==0.22.0
- scipy==1.1.0
- scikit-learn==0.19.1
- jupyter==1.0.0
file
Conda environments make development easier
Dr. Miguel Fierro - @miguelgfierro

9. Typical project structure
9
docs
robotics
tests
third_party
tools
.coveragerc
.gitignore
.travis.yml
LICENSE.md
README.md
setup.py
Example of library: robotics

10. 10
Agenda
The why, the what and the how of Python
Development
strategies
Software development principles
What’s next?

11. 11
Jupyter notebooks
Dr. Miguel Fierro - @miguelgfierro

12. Test Driven Development
Develop the tests first
1) Add a test
Write a test that defines a function or
improvements of a function.
It makes the developer focus on the
requirements before writing the code, a
subtle but important difference.
2) Run the test to check it fails
Execute all the tests and check whether
they pass or fail. The new test should fail
for the expected reason.
3) Write the code
Write some code that causes the test to
pass. The new code written at this stage is
not perfect and will be improved later.
At this point, the only purpose of the
written code is to pass the test.
5) Refactor code
Clean the code, remove duplication, avoid
magic numbers (constants without a
variable) and apply other software
development techniques.
4) Run the test to check it passes
The new test should pass.
Now the programmer can be confident
that the new code meets the test
requirements.
6) Repeat
For each new functionality of the code,
start by adding a new test
Dr. Miguel Fierro - @miguelgfierro

13. 13
def test_predict_accuracy (self):
acc = predict()
self.assertGreaterEqual(acc, 0)
self.assertLessEqual(acc, 1)
Type of tests
Python def test_predict_accuracy (self):
acc = predict()
self.assertGreaterEqual(acc, 0.65)
def test_predict_accuracy (self):
acc = predict()
self.assertEqual(acc, 0.654345675)
Unit tests Integration tests Utility tests
It tests the correct behavior It tests that whether the result is acceptable It shows an example of the behavior
Dr. Miguel Fierro - @miguelgfierro

14. 14
How to create a library
Dr. Miguel Fierro - @miguelgfierro

15. 15
def sigmoid(x):
"""Sigmoid function. Output between 0-1
Args:
x (np.array): An array.
Returns:
result (np.array): Sigmoid of the array.
Examples:
>>> x = np.array([[1,1,-3],[0.5,-1,1]])
>>> sigmoid(x)
array([[0.73, 0.73, 0.04],
[0.62, 0.26, 0.73]])
"""
return 1. / (1 + np.exp(-x))
Documentation: Python docstrings
Python
Google style Numpy style
def sigmoid(x):
"""Sigmoid function. Output between 0-1
Parameters
-----------
x : np.array
An array.
Returns
-------
result : np.array
Sigmoid of the array.
Examples
--------
>>> x = np.array([[1,1,-3],[0.5,-1,1]])
>>> sigmoid(x)
array([[0.73, 0.73, 0.04],
[0.62, 0.26, 0.73]])
"""
return 1. / (1 + np.exp(-x))
Dr. Miguel Fierro - @miguelgfierro

16. 16
Code style: PEP8
Python's official style guide, for formatting code
correctly to maximize its readability.
Created in 2001 by Guido van Rossum et. al.
!DILEMMA:
How to automatize the code style?
Use auto-format in your favorite IDE

17. PyCharm
Free and payed
version
Visual Studio
Heavy weight IDE with
many functionalities
VS Code
Ubuntu default
Atom
Results visualization
No matter which IDE you prefer,
it will save you time and make the
development easier.
Dr. Miguel Fierro - @miguelgfierro

18. 18
Agenda
The why, the what and the how of Python
Development
strategies
Software development principles
What’s next?

19. Software development principles
Single responsibility DRY
(Don’t Repeat
Yourself)
MVP
(Minimum Viable
Product)
Plan for reuse
Key concepts for creating great software
Dr. Miguel Fierro - @miguelgfierro

20. Modularity
Single responsibility
Each class or module should be responsible for a
single part of the software, in other words: “A
class should have only one reason to change”.
Part of a broader set of principles called SOLID.
A class does only one thing, a function does only one thing
Dr. Miguel Fierro - @miguelgfierro

21. DRY
If a piece of code can be generalized and reuse, do it!
Extract a new function or a private method.
Reducing complexity
Don’t Repeat Yourself … please
Dr. Miguel Fierro - @miguelgfierro

22. Fail fast
MVP
The MVP is the minimum product that collects the
maximum amount of validated learning about
customers with the least effort.
Based on the Lean Startup methodology.
Minimum Viable Product
Dr. Miguel Fierro - @miguelgfierro

23. Generalize your code to be reusable
Generalization
Plan for reuse
Whenever you create a piece of software, design it
in a way so it can be reusable in other projects.
It will save you a lot of time.
Dr. Miguel Fierro - @miguelgfierro

24. 24
Agenda
The why, the what and the how of Python
Development
strategies
Software development principles
What’s next?

25. 25
Create your own codebase
Dr. Miguel Fierro - @miguelgfierro

26. 26
Start contributing to opensource
Dr. Miguel Fierro - @miguelgfierro

27. Dr. Miguel Fierro
@miguelgfierro
Best practices in coding for
beginners