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An Introduction to Python�A general-purpose, easy-to-use open-source Programming Language

Telefon: +43 3842 402 - 1901 �Email: teaching@ai-lab.science

Univ.-Prof. Dr. Elmar Rueckert�

WO AUS FORSCHUNG ZUKUNFT WIRD

Chair of Cyber-Physical-Systems

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Topics of this tutorial

1. What is Python?

2. Why should you learn Python?

3 . Installation Instructions.

4 . Structure of Python files and the __name__ attribute.

5 . Clean Coding Principles.

6 . Learning by Doing: Literature.

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What is Python?

Python is a general purpose programming language.

Python was invented by Guido van Rossum starting in 1989 as an easy-to-use open-source language.

Python supports object-oriented concepts and since 2000 it uses a Garbage-Collector for the memory management.

Python uses the feature Indentation to structure the code:

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Why Python?

Easy-to-use and open-source.

Many tutorial and online resources, e.g., https://pythonbasics.org/.

Python is the most popular programming language, see the statistics from 2019-2020 on the right.

We use Python together with the Robot-Operating-System (ROS) to re-use algorithms with different sensors, actuators or robots.

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Topics of this tutorial

1. What is Python?

2. Why should you learn Python?

3. Installation Instructions.

4. Structure of Python files and the __name__ attribute.

5. Clean Coding Principles.

6. Learning by Doing: Literature.

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Installation Instructions

GNU / Linux:

Python is typically pre-installed. Check your version typing python -V in the command line.

Mac OS:

Python 2.x is pre-installed. Python 3.x can be installed using Homebrew for example. Check your version typing python -V in the command line.

Windows:

Download a 32 or 64 bit Windows installer from https://www.python.org/downloads/windows/
During the installation, make sure to check the box to add the location python.exe to your path.
Alternatively, add adapt the path manually.

Test your Installation:

Open a Terminal and type: python3
Type print("Hello World") and press ENTER
Type 3+7 and press ENTER
Run �import sys

print("Current version of Python is ", sys.version)

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Installing Packages

In PyCharm (here is a guide):

When creating a new project, select virtual environment for the packages.
After adding an import command to your code file, an error will appear.
Click on the error symbol and select install package.

Manually using conda or PIP (here is a guide):

Type pip install numpy in a terminal. You may want to do that in a python environment to avoid installing wrong package versions for your python version.

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Array / Matrix Calculus Support

Per default python does not support array or matrix operations or functions. Install NUMPY for that.

Some NUMPY Features:

See https://pythonexamples.org/numpy/ for details.

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Topics of this tutorial

1. What is Python?

2. Why should you learn Python?

3. Installation Instructions.

4. Structure of Python files and the __name__ attribute.

5. Clean Coding Principles.

6. Learning by Doing: Literature.

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Structure of a Python File

Line 1: The shebang command denoting which Python Interpreter version is required.

Line 8-11: Some informative description of what this file is doing.

Line 13-16: List of all imported packages (sys and numpy) and also of all imported modules (e.g., using import my_file_two)

Line 18-20: Definition of a function without any arguments.

Line 18-20: Definition of a function with one argument.

Line 28-33: Main section of the code. The interpreter assigns the name ‘__main__’ to the executed script when you execute python main.py

Line 34-38: First the two function calls are executed, followed by the creation of an array. In line 38, the array is printed in the output window.

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Topics of this tutorial

1. What is Python?

2. Why should you learn Python?

3. Installation Instructions.

4. Structure of Python files and the __name__ attribute.

5. Clean Coding Principles.

6. Learning by Doing: Literature.

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Clean Coding Principles

https://testdriven.io/blog/clean-code-python/

Clean code is a set of rules and principles that helps to keep our code readable, maintainable, and extendable. It's one of the most important aspects of writing quality software. We (developers) spend way more time reading the code than actually writing it, which is why it's important that we write good code.

Writing code is easy, but writing good, clean code is hard.

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We follow the PEP 8 (Python Enhancement Proposal)

https://www.python.org/dev/peps/pep-0008/

PEP 8 naming conventions:

class names should be CamelCase (MyClass)
variable names should be snake_case and all lowercase (first_name)
global variable names should be avoided, however use all upper_case (MY_GLOBAL_COUNTER)
function names should be snake_case and all lowercase (quick_sort())
constants should be snake_case and all uppercase (PI = 3.14159)
modules should have short, snake_case names and all lowercase (numpy)
single quotes and double quotes are treated the same (just pick one and be consistent)

# This is bad

# represents the number of active users

au = 55

# This is good

active_user_amount = 55

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We follow the PEP 8 (Python Enhancement Proposal)

https://www.python.org/dev/peps/pep-0008/

PEP 8 line formatting:

indent using 4 spaces (spaces are preferred over tabs)
lines should not be longer than 79 characters
avoid multiple statements on the same line
top-level function and class definitions are surrounded with two blank lines
method definitions inside a class are surrounded by a single blank line
imports should be on separate lines

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We follow the PEP 8 (Python Enhancement Proposal)

https://www.python.org/dev/peps/pep-0008/

PEP 8 whitespace:

avoid extra spaces within brackets or braces
avoid trailing whitespace anywhere
always surround binary operators with a single space on either side
if operators with different priorities are used, consider adding whitespace around the operators with the lowest priority
don't use spaces around the = sign when used to indicate a keyword argument

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We follow the PEP 8 (Python Enhancement Proposal)

https://www.python.org/dev/peps/pep-0008/

PEP 8 comments:

comments should not contradict the code
comments should be complete sentences
comments should have a space after the # sign with the first word capitalized
multi-line comments used in functions (docstrings) should have a short single-line description followed by more text

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Examples

# This is bad

# represents the number of active users

au = 55

# This is good

active_user_amount = 55

Naming Conventions:

# This is bad

c = 5

d = 12

# This is good

city_counter = 5

elapsed_time_in_days = 12

Use descriptive names:

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Examples

from datetime import datetime

# This is bad

genyyyymmddhhmmss = datetime.strptime('04/27/95 07:14:22', '%m/%d/%y %H:%M:%S')

# This is good

generation_datetime = datetime.strptime('04/27/95 07:14:22', '%m/%d/%y %H:%M:%S')

Use pronounceable names:

# This is bad

fna = 'Bob'

cre_tmstp = 1621535852

# This is good

first_name = 'Bob'

creation_timestamp = 1621535852

Avoid using ambiguous abbreviations:

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Examples

# This is bad

client_first_name = 'Bob'

customer_last_name = 'Smith'

# This is good

client_first_name = 'Bob'

client_last_name = 'Smith'

Use consistent vocabulary:

import random

# This is bad

def roll():

return random.randint(0, 36) # what is 36 supposed to represent?

# This is good

ROULETTE_POCKET_COUNT = 36

def roll():

return random.randint(0, ROULETTE_POCKET_COUNT)

Don’t use magic numbers:

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Examples

# This is bad

class Person:

def __init__(self, person_first_name, person_last_name, person_age):

self.person_first_name = person_first_name

self.person_last_name = person_last_name

self.person_age = person_age

# This is good

class Person:

def __init__(self, first_name, last_name, age):

self.first_name = first_name

self.last_name = last_name

self.age = age

Use Constructors and avoid redundancies:

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Examples

# This is bad

def fetch_and_display_personnel():

data = # ...

for person in data:

print(person)

# This is good

def fetch_personnel():

return # ...

def display_personnel(data):

for person in data:

print(person)

Functions should only perform a single task:

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Examples

# This is bad

def render_blog_post(title, author, created_timestamp, updated_timestamp, content):

# ...

render_blog_post("Clean code", "Nik Tomazic", 1622148362, 1622148362, "...")

# This is good

class BlogPost:

def __init__(self, title, author, created_timestamp, updated_timestamp, content):

self.title = title

self.author = author

self.created_timestamp = created_timestamp

self.updated_timestamp = updated_timestamp

self.content = content

blog_post1 = BlogPost("Clean code", "Nik Tomazic", 1622148362, 1622148362, "...")

def render_blog_post(blog_post):

# ...

render_blog_post(blog_post1)

Use Classes to keep the number of arguments at a minimum:

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Examples

# This checks if the user with the given ID doesn't exist.

if not User.objects.filter(id=user_id).exists():

return Response({

'detail': 'The user with this ID does not exist.',

})

As a general rule, if you need to add comments, they should explain "why" you did something rather than "what" is happening:

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Hints: Use Context Manager to read files

with open('wisdom.txt', 'w') as opened_file:

opened_file.write('Python is cool.')

# opened_file has been closed.

Read files using the ‘with’ statement:

file = open('wisdom.txt', 'w')

try:

file.write('Python is cool.')

finally:

file.close()

Avoid

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Topics of this tutorial

1. What is Python?

2. Why should you learn Python?

3. Installation Instructions.

4. Structure of Python files and the __name__ attribute.

5. Clean Coding Principles.

6. Learning by Doing: Literature.

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Learning by Doing

Introductions:

Wikis, Tutorials & Videolectures:

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Thank you for your attention!

Univ.-Prof. Dr. Elmar Rückert

Chair of Cyber-Physical-Systems

Montanuniversität Leoben

Franz-Josef-Straße 18,

8700 Leoben, Austria

Phone: +43 3842 402 – 1901 (Sekretariat CPS)

Email: teaching@ai-lab.science

Web: https://cps.unileoben.ac.at

Disclaimer: The lecture notes posted on this website are for personal use only. The material is intended for educational purposes only. Reproduction of the material for any purposes other than what is intended is prohibited. The content is to be used for educational and non-commercial purposes only and is not to be changed, altered, or used for any commercial endeavor without the express written permission of Professor Rueckert.

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