1.4. Python Language

Figure 1.1. Python Logo

1.4.1. Rationale

• Turing complete, general purpose language

• Multi platform

• Dynamic typing with automatic memory allocation and GC

• Code readability and simplicity is important

• White space are important

• Everything is an object, but you can write functional code too

• Standard language in Machine Learning and Data Science

• Very good standard system library

• Huge ecosystem of external open source libraries

• Open Source created by non-profit Python Software Foundation

1.4.2. Which Version?

• You should use newest official Python version

Table 1.2. Future Versions

Version	PEP	Status	Release	End-of-life	Release Manager
3.10	TBA	future	2020-10-05	2025-10	TBA
3.9	PEP 596	development	2020-10-05	2025-10	Łukasz Langa

Table 1.3. Currently Supported Versions

Version	PEP	Status	Release	End-of-life	Release Manager
3.8	PEP 569	features	2019-10-20	2024-10	Łukasz Langa
3.7	PEP 537	bugfix	2018-06-27	2023-06-27	Ned Deily
3.6	PEP 494	security	2016-12-23	2021-12-23	Ned Deily
3.5	PEP 478	security	2015-09-13	2020-09-13	Larry Hastings

Table 1.4. Unsupported Versions

Version	PEP	Status	Release	End-of-life	Release Manager
3.4	PEP 429	end of life	2014-03-16	2019-03-16	Larry Hastings
3.3	PEP 398	end of life	2012-09-29	2017-09-29	Georg Brandl
3.2	PEP 392	end of life	2011-02-20	2016-02-20	Georg Brandl
3.1	PEP 375	end of life	2009-06-27	2012-04-09	Benjamin Peterson
3.0	PEP 361	end of life	2008-12-03	2009-01-13	Barry Warsaw
2.7	PEP 373	end of life	2010-07-03	2020-04-20	Benjamin Peterson
2.6	PEP 361	end of life	2008-10-01	2013-10-29	Barry Warsaw

1.4.3. Why not Python 2?

• 2020-04-20 - end of Life for Python 2.7 PEP 373

• Python 2 is no longer developed [1, 2]

• Python 2.7 is the last in 2.x branch, and there won't be Python 2.8 PEP 404

• Python 2.7.18, the last release of Python 2 [3]

1.4.4. Changes in Python 3

• All strings are Unicode

• In Python 3 print() is a function, not a keyword

• Changes in standard library modules naming and location

• New string formatting

1.4.5. Python Release Cycle

New in version Python: 3.9 See PEP 602

• 12 months (1 year) release cycle

• 18 months (1.5 year) of bugfix updates

• 42 months (3.5 year) of security updates

Figure 1.2. Python 12 months release cycle.

1.4.6. Scripts

• Python files use .py as an extension

• Compiled files are in __pycache__ directory

• Python also uses other extensions

Table 1.5. Python file types and extensions

Extension	Description
.pyc	Compiled source code (bytecode)
.pyd	Compiled Windows DLL file
.pyw	Compiled Windows file. Executable with pythonw.exe
.pyx	cPythona source for C/C++ conversion
.pyz	zipapp compressed archive. Since Python 3.5

Listing 1.1. Minimal script

print('Ehlo World!')

1.4.7. Python Console (REPL)

• Read–Eval–Print Loop

• Quickly test and evaluate code

• Lines starts with >>>

• Line continuation starts with ...

• Result is printed below

• Open REPL with python3 command in terminal

$ python3
3.8.2 (default, Mar 11 2020, 00:29:50)
[Clang 11.0.0 (clang-1100.0.33.17)]
Type "help", "copyright", "credits" or "license" for more information.

>>> print('Ehlo World!')
Ehlo World!

Note

In documentation and books you may find >>> and ... at the beginning of code listing lines

>>> if True:
...     print('yes')
... else:
...     print('no')
yes

1.4.8. Jupyter

• Open Source web application REPL

• Very popular in Machine Learning and Data Science world

• Create and share documents that contain live code, equations, visualizations and narrative text

• Uses include: data cleaning and transformation, numerical simulation, statistical modeling, data visualization, machine learning, etc

1.4.9. Python Developer Survey

• Annual survey

• https://www.jetbrains.com/lp/python-developers-survey-2019

1.4.10. Assignments

1.4.10.1. Check Python Version

• Complexity level: easy

• Lines of code to write: 0 lines

• Estimated time of completion: 5 min

• Solution: solution/about_version.py

English

1. Create file wih name about_version.py

2. Use code from "Input" section (see below)

3. Run code in your IDE (right click on code -> "Run File in Python Console")

4. What Python version is installed?

5. Newest official Python is recommended

6. Compare result with "Output" section (see below)

Polish

1. Stwórz skrypt o nazwie about_version.py

2. Użyj kodu z sekcji "Input" (patrz poniżej)

3. Uruchom kod swoim IDE (prawy klawisz myszy na kodzie -> "Run File in Python Console")

4. Jaka wersja Python jest zainstalowana?

5. Zalecana jest najnowasza oficjalna wersja Python

6. Porównaj wyniki z sekcją "Output" (patrz poniżej)

Input

import sys

print(sys.version)

Output

3.8.2 (default, Mar 11 2020, 00:29:50)
[Clang 11.0.0 (clang-1100.0.33.17)]

The whys and wherefores

• Czy Python działa

• Jaka jest wersja Python

• Korzystanie z print

• Umiejętność uruchamiania skryptów

• Szukanie rozwiązań zadań z książki

1.4.10.2. Check Python Environment

• Complexity level: easy

• Lines of code to write: 0 lines

• Estimated time of completion: 5 min

• Solution: solution/about_env.py

1. Stwórz plik o nazwie about_env.py

2. Plik ma mieć zawartość:

   import sys
   import os
   
   print(f'Python Executable: {sys.executable}')
   print(f'Python Version: {sys.version}')
   print(f'Virtualenv: {os.getenv("VIRTUAL_ENV")}')
   

3. Uruchom go w swoim IDE (menu Run -> Run... -> nazwa Twojego skryptu)

4. Gdzie Python jest zainstalowany?

5. Czy korzystasz z "Virtualenv"?

6. Upewnij się, że w linijce z "Virtualenv" nie masz None

The whys and wherefores

• Czy Python działa

• Jaka jest wersja Python

• Czy korzystasz z Virtualenv

• Korzystanie z print

• Umiejętność uruchamiania skryptów

• Szukanie rozwiązań zadań z książki