1.3. Python Language

• 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

Figure 1.1. Python Logo

1.3.1. Which Version?

• You should use newest official Python version 4

• Source: https://devguide.python.org/#status-of-python-branches

• Source: https://www.python.org/downloads/

Table 1.2. Python Versions 4

Version	PEP	Status	Release	End-of-life	Release Manager
3.12	TBA	future	2023-10	2028-10	TBA
3.11	PEP 664	features	2022-10-03	2027-10	Pablo Galindo Salgado
3.10	PEP 619	bugfix	2021-10-04	2026-10	Pablo Galindo Salgado
3.9	PEP 596	bugfix	2020-10-05	2025-10	Łukasz Langa
3.8	PEP 569	security	2019-10-20	2024-10	Łukasz Langa
3.7	PEP 537	security	2018-06-27	2023-06-27	Ned Deily
3.6	PEP 494	end-of-life	2016-12-23	2021-12-23	Ned Deily
3.5	PEP 478	end-of-life	2015-09-13	2020-09-13	Larry Hastings
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

features

new features, bugfixes, and security fixes are accepted.

prerelease

feature fixes, bugfixes, and security fixes are accepted for the upcoming feature release.

bugfix

bugfixes and security fixes are accepted, new binaries are still released. (Also called maintenance mode or stable release)

security

only security fixes are accepted and no more binaries are released, but new source-only versions can be released

end-of-life

release cycle is frozen; no further changes can be pushed to it.

1.3.2. Why not Python 2?

• PEP 373 -- Python 2.7 Release Schedule

• PEP 404 -- Python 2.8 Un-release Schedule

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

• 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

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

1.3.3. 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

1.3.4. Python Release Cycle

• Since Python 3.9: PEP 602 -- Annual Release Cycle for Python

• 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.

1.3.5. Scripts

• Python files use .py as an extension

• Compiled files are in __pycache__ directory

• Python also uses other extensions

Table 1.3. 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

1.3.6. 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

$ python3.10
Python 3.10.0 (default, Oct 13 2021, 06:45:00) [Clang 13.0.0 (clang-1300.0.29.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>
>>> print('Ehlo World!')
Ehlo World!

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

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

1.3.7. 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

1.3.8. Python Developer Survey

• Annual survey

• https://www.jetbrains.com/lp/python-developers-survey-2020/

• https://www.jetbrains.com/lp/devecosystem-2020/python/

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

• https://www.jetbrains.com/research/python-developers-survey-2018/

• https://www.jetbrains.com/research/python-developers-survey-2017/

• https://insights.stackoverflow.com/survey/2020

• https://insights.stackoverflow.com/survey/2019

• https://insights.stackoverflow.com/survey/2018

1.3.9. References

4(1,2)

https://devguide.python.org/#status-of-python-branches

1.3.10. Assignments

Code 1.3. Solution

"""
* Assignment: About Environment
* Complexity: easy
* Lines of code: 0 lines
* Time: 3 min

English:
    1. Create file `about_env.py`
    2. Run file in your IDE
    3. Where Python is installed?
    4. Are you using "venv"?
    5. Make sure, `venv` is not `None`
    6. Run doctests - all must succeed

Polish:
    1. Stwórz plik `about_env.py`
    2. Uruchom plik w swoim IDE
    3. Gdzie Python jest zainstalowany?
    4. Czy korzystasz z "venv"?
    5. Upewnij się, że `venv` nie jest `None`
    6. Uruchom doctesty - wszystkie muszą się powieść

Tests:
    >>> import sys; sys.tracebacklimit = 0

    >>> assert python_executable
    >>> assert python_version
"""

import os
import sys


python_executable = sys.executable
python_version = tuple(sys.version_info)
venv = os.getenv("VIRTUAL_ENV")