1.3. Python Language¶

Figure 1.1. Python Logo¶

1.3.1. 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

1.3.2. Which Version?¶

You should use newest official Python version
Source: https://devguide.python.org/#status-of-python-branches
Source: https://www.python.org/downloads/

Table 1.2. Future Versions¶
Version	PEP	Status	Release	End-of-life	Release Manager
3.11	TBA	future	2022-10-04	TBA	Pablo Galindo Salgado
3.10	TBA	development	2021-10-04	TBA	Pablo Galindo Salgado

Table 1.3. Currently Supported Versions¶
Version	PEP	Status	Release	End-of-life	Release Manager
3.9	PEP 596	features	2020-10-05	TBA	Łukasz Langa
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

Table 1.4. Unsupported Versions¶
Version	PEP	Status	Release	End-of-life	Release Manager
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

1.3.3. 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]

1.3.4. 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

1.3.5. 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

../../_images/pep602-release-calendar.png — Figure 1.2. Python 12 months release cycle.¶

1.3.6. 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

1.3.7. 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!

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

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

1.3.8. 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

1.3.9. Python Developer Survey¶

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")