PEP20:The Zen of Python

>>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it.
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
>>>

PEP 20 -- The Zen of Python

PEP 20 (The Zen of Python) by Example by Hunter Blank

PEP8: Style Guide for Python Code

PEP8 is the de facto coding style guide for Python.

PEP 8 @python.org

Indentation

def long_function_name(
        var_one, var_two, var_three,
        var_four):
    print(var_one)

#Arguments on first line forbidden when not using vertical alignment.
def long_function_name(var_one, var_two, var_three,
        var_four):
    print(var_one)

Indentation

my_list = [
    1, 2, 3,
    4, 5, 6,
]

my_list = [
    1, 2, 3,
    4, 5, 6,
          ]

Line break before or after a binary operator?

result = (op1
          + (op2 * op3)
          - op4)

result = (op1 +
          op2 *
          op3 -
          op4)

Tabs or Spaces?

Spaces are the preferred indentation method.

Python 3 disallows mixing the use of tabs and spaces for indentation.

pycodestyle - example

def print_list(my_list):
  for i in my_list:
    print(i)
my_list = [
          1, 2, 3,
          4, 5, 6,]

print_list(my_list)

$ pycodestyle nonPEP8_styled.py
nonPEP8_styled.py:2:3: E111 indentation is not a multiple of four
nonPEP8_styled.py:4:1: E305 expected 2 blank lines after class or function definition, found 0
nonPEP8_styled.py:6:18: E231 missing whitespace after ','
nonPEP8_styled.py:8:20: W292 no newline at end of file

pycodestyle for Editors and IDEs

SublimeLinter-pycodestyle

Pep8 Linting @code.visualstudio.com

PyCharm - you can set pycodestyle as an external tool

Project Documentation for Contributors

A README file at the root directory should give general information to both users and maintainers of a project

A LICENSE file should always be present and specify the license under which the software is made available to the public.

A TODO file (or section in README) should list the planned development for the code.

A CHANGELOG file (or section in README) should present a short overview of the changes in the code base for the latest versions.

Python documentation tools

Sphinx - is a tool that makes it easy to create intelligent and beautiful documentation

Sphinx is well integrated with Read The Docs - free documentation hosting for the open source community

Best Practices for testing

A testing unit should focus on one tiny bit of functionality and prove it correct.

Each test unit must be fully independent: able to run alone and regardless of the order the test units are called

Use long and descriptive names for testing function, as these function names are displayed when a test fails.

Try hard to make tests that are fast

Always run the full test suite before a coding session, and run it again after.

unittest - Python's Unit testing framework

The built-in module unittest implements unit testing framework in Python, similar to JUnit or nUnit

Creating test cases is accomplished by subclassing unittest.TestCase

Test methods must start with the string test or they will not run.

Test modules (files) are expected to match the pattern test*.py by default, or the --pattern keyword argument, if given, on the command line

unittest - example

import unittest

def floor_div(x,y):
  return x/y

class PositiveTest(unittest.TestCase):
  def test_floor_div_with_positive_integers(self):
    self.assertEqual(floor_div(4,3), 1)

$ python3 -m unittest floor_div_test.py
F
======================================================================
FAIL: test_floor_div_with_positive_integers (floor_div_test.PositiveTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/data/projects/www/wwwcourses.github.io/ProgressBG-VC2-Python/pages/themes/beginners/practicalities/examples/floor_div_test.py", line 9, in test_floor_div_with_positive_integers
    self.assertEqual(floor_div(4,3), 1)
AssertionError: 1.3333333333333333 != 1

----------------------------------------------------------------------
Ran 1 test in 0.000s

FAILED (failures=1)

Example

def floor_div(x,y):
  return x/y

def test_floor_div_with_positive_integers():
  assert floor_div(4,3) == 1

>pytest floor_div_pytest.py
========================================================================= test session starts =========================================================================
platform linux -- Python 3.6.4, pytest-3.5.0, py-1.5.3, pluggy-0.6.0
rootdir: /data/projects/www/wwwcourses.github.io/ProgressBG-VC2-Python/pages/themes/beginners/practicalities/examples, inifile: pytest.ini
collected 1 item

floor_div_pytest.py F                                                                                                                                           [100%]

============================================================================== FAILURES ===============================================================================
________________________________________________________________ test_floor_div_with_positive_integers ________________________________________________________________

    def test_floor_div_with_positive_integers():
>     assert floor_div(4,3) == 1
E     assert 1.3333333333333333 == 1
E      +  where 1.3333333333333333 = floor_div(4, 3)

floor_div_pytest.py:6: AssertionError
====================================================================== 1 failed in 0.03 seconds =======================================================================

Customizing test collection

# discover tests from every Python file
[pytest]
python_files = *.py

$pytest --collect-only
========================================================================= test session starts =========================================================================
platform linux -- Python 3.6.4, pytest-3.5.0, py-1.5.3, pluggy-0.6.0
rootdir: /data/projects/www/wwwcourses.github.io/ProgressBG-VC2-Python/pages/themes/beginners/practicalities/examples, inifile: pytest.ini
collected 3 items
<Module 'floor_div_pytest.py'>
  <Function 'test_floor_div_with_positive_integers'>
<Module 'floor_div_test.py'>
  <UnitTestCase 'PositiveTest'>
    <TestCaseFunction 'test_floor_div_with_positive_integers'>
<Module 'pytest_sample.py'>
  <Function 'test_answer'>

==================================================================== no tests ran in 0.01 seconds =====================================================================
(ProgressBG-VC2-Python)nemsys@X230~gh-pages->

Videos

Raymond Hettinger - Beyond PEP 8 -- Best practices for beautiful intelligible code - PyCon 2015