Anthony Shaw - Wily Python: Writing simpler and more maintainable Python

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Wily Python: Writing simpler and more maintainable Python Anthony Shaw @anthonypjshaw

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Is my code complicated? By what measure? How do I simplify it?

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Introduction Is my code complicated? By what measure? How do I simplify it? Beginner Level Intermediate to Advanced

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Lines of code

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Fewer lines doesn’t mean less complexity

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“ Readability counts ” — Tim Peters

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Cyclomatic Complexity Make it a meal? Small, large or super-size? What drink? Diet or regular? Yes Large Cola Diet * Other burgers are available +1 +1 +1 +1 Big Mac please *

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There’s wisdom in complex code

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Functionality More Less Less More Users ! Lines of Code "Cyclomatic Complexity " Lines of Code "Cyclomatic Complexity ! Lines of Code ! Cyclomatic Complexity " Lines of Code ! Cyclomatic Complexity

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Halstead Metrics Warning: This chapter contains math

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Values Variables Operands ∑ ∑ Built in syntax Operators ∑ Operators and Operands

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Length and Vocabulary operators operands Vocabulary (h) ∃! ∃! operators operands Length (N) ∑ ∑

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def foo(): a = 1 b = a + 1 return b Halstead in the AST

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Volume and Difficulty Better than LoC Length (N) Vocab (h) Volume (V) !"#$ operators operands Difficulty (D) ∃! 2 operands ∃! ∑ A great compliment to CC

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Effort Volume Difficulty Effort (E) operators operands ∃! 2 operands ∃! ∑ Length (N) Vocab (h) "#$%

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Maintainability Index 0-25 25-50 50-75 75-100 MI = 171 − 5.2 ln , − 0.23 / − 16.2 ln(2) Halstead Volume Cyclomatic Complexity LoC Unmaintainable Cause for concern Needs improvement Super-hero code

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Radon $ pip install radon $ radon cc my_application.py -s my_application.py F 4:0 main - B (6) $ radon mi my_application.py -s my_application.py - A (87.42)

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$ radon hal my_application.py my_application.py: h1: 3 h2: 6 N1: 3 N2: 6 vocabulary: 9 length: 9 calculated_length: 20.264662506490406 volume: 28.529325012980813 difficulty: 1.5 effort: 42.793987519471216

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Cache Revisions Operators Indexes Git Repo wily build

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Demo of wily

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Complexity has gravity app.py

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Testing and refactoring •High test coverage should be a given •Test coverage is not an indicator of behavioral coverage •Fixing known bugs is hard

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• Wily can benefit you in tracking complexity • Complexity Measures are long-term • Make sure you have good behavioral test coverage • Refactor often • Divide and conquer Talk notes

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Thanks! realpython.com/python-refactoring [email protected] @anthonypjshaw tonybaloney.github.io