@KNerush @Volodymyrk

Clean CodeIn Jupyter notebooks, using Python

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5th of July, 2016

@KNerush @Volodymyrk

Volodymyr (Vlad) Kazantsev

Head of Data @ product madness

Product Manager

MBA @LBS

Graphics programming

Writes code for money since 2002

Math degree2

Kateryna (Katya) Nerush

Mobile Dev @ Octopus Labs

Dev Lead in Finance

Data Engineer

Web Developer

Writes code for money since 2003

CS degree

@KNerush @Volodymyrk

Why we end-up with messy ipy notebooks?

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Coding

Stats Business

@KNerush @Volodymyrk

Who are Data Scientists, really?

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Coding

Stats Business “In a nutshell, coding is telling a computer to do something using a language it understands.”

Data Science with Python

@KNerush @Volodymyrk

It is not going to production anyway!

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@KNerush @Volodymyrk

“Any fool can write code that a computer can understand. Good programmers write code that humans can understand” - Kent Beck, 1999

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WTF! How am I suppose to validate this??

Sorry, but how do can I calculate 7 day retention ?

@KNerush @Volodymyrk

From Prototype to ... The Data Science Spiral

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Ideas & Questions

Data Analysis

Insights

Impact

@KNerush @Volodymyrk

You do it for your own good..

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Re-run all AB tests analysis for the last months, by tomorrow

Ideas & Questions

Data Analysis

Insights

Impact

@KNerush @Volodymyrk

Part 2What can Data Scientists learn from

Software Engineers?

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@KNerush @Volodymyrk

Robert C. Martin, a.k.a. “Uncle Bob”

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https://cleancoders.com/

@KNerush @Volodymyrk

“Clean Code” ?

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Pleasingly graceful and stylish in appearance or manner

Bjarne StroustrupInventor of C++

Clean code reads like well written proseGrady Boochcreator of UML

.. each routine turns out to be pretty much what you expected

Ward Cunninghaminventor of Wiki and XP

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One does not simply start writing clean code..

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First make it work,Then make it Right,Then make it fast and small

Kent Beckco-inventor of XP and TDD

Leave the campground cleaner than you found it

- Run all the tests

- Contains no duplicate code

- Expresses all ideas...

- Minimize classes and methods

Ron Jeffriesauthor of Extreme

Programming Installed

The Boy Scouts of America

Applied to programming by Uncle Bob

@KNerush @Volodymyrk

I'm not a great programmer; I'm just a good programmer with great habits.

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Kent Beck

@KNerush @Volodymyrk

“There are only two hard problems in Computer Science: cache invalidation and naming things" - Phil Karlton

long_descriptive_names

Avoid: x, i, stuff, do_blah()

Pronounceable and Searchable

revenue_per_payer vs. arpdpu

Avoid encodings, abbreviations, prefixes, suffixes.. if possible bonus_points_on_iphone vs. cns_crm_dip

Add meaningful contextdaily_revenue_per_payer

Don’t be lazy. Spend time naming and renaming things.14

@KNerush @Volodymyrk

“each routine turns out to be pretty much what you expected” - Ward Cunningham

Small

Do one thing

One Level of Abstraction

Have only few arguments (one is the best)

Less important in Python, with named arguments.

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@KNerush @Volodymyrk

Use good names

Avoid obvious comments.

Dead Commented-out Code

ToDo, licenses, history, markup for documentation and other nonsense

But there are exceptions..

“When you feel the need to write a comment, first try to refactor the code so that any comment becomes superfluous” Kent Beck

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@KNerush @Volodymyrk

// When I wrote this, only God and I understood what I was doing// Now, God only knows

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@KNerush @Volodymyrk

// sometimes I believe compiler ignores all my comments

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@KNerush @Volodymyrk

/*** Always returns true.*/public boolean isAvailable() { return false;}

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@KNerush @Volodymyrk

“Long functions is where classes are trying to hide” - Robert C. Martin

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Small

Do one thing

SOLID, Design Patterns, etc.

@KNerush @Volodymyrk

Code conventions

Team should produce same style code as if that was one person

Team conventions over language one, over personal ones

Automate style formatting

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@KNerush @Volodymyrk

Part 3How to write Clean Code in Python?

(e.g. this is not Java)

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@KNerush @Volodymyrk

● Indentation● Tabs or Spaces?● Maximum Line Length● Should a line break before or after a binary operator?● Blank Lines● Imports● Comments● Naming Conventions

Example:

PEP 8 -- Style Guide for Python Code

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foo = long_function_name(var_one, var_two, var_three, var_four)

foo = long_function_name(var_one, var_two, var_three, var_four)

Good Bad

https://www.python.org/dev/peps/pep-0008/

@KNerush @Volodymyrk

Google Python Style Guide

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https://google.github.io/styleguide/pyguide.html

@KNerush @Volodymyrk25

My favourite !

This is not Java or C++

Functions are first-class objects

Duck-typing as an interface

No setters/getters

Itertools, zip, enumerate

etc.

@KNerush @Volodymyrk

Part 4How to write Clean Python Code in

Jupyter Notebook?

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@KNerush @Volodymyrk

1. Imports

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2. Get Data

5.Visualisation

6. Making sense of the data

4. Modelling

3. Transform Data

Typical structure of the ipynb

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How big should a notebook file be?

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@KNerush @Volodymyrk

How big should a notebook file be?

Hypothesis - Data - Interpretation

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@KNerush @Volodymyrk

Keep your notebooks small!

(4-10 cells each)

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@KNerush @Volodymyrk

Example:

Tip 1: break fat notebook into many small ones

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1_data_preparation.ipynb

df.to_pickle(‘clean_data_1.pkl)

2_linear_model.py

df = pd.read_pickle(‘clean_data_1.pkl)

3_ensamble.py

df = pd.read_pickle(‘clean_data_1.pkl)

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Tip 2: shared library

Data access

Common plotting functionality

Report generation

Misc. utils

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acme_data_utils Data_access.py plotting.py setup.py tests/

@KNerush @Volodymyrk

Tip 3: Don’t just be pythonic. Be IPythonicDon’t hide “secret sauce” inside imported module

BAD:

Good:

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@KNerush @Volodymyrk

Clean code reads like well written prose

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Grady Booch

@KNerush @Volodymyrk

Good jupyter notebook reads like well written prose

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@KNerush @Volodymyrk

How big should one Cell be?

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@KNerush @Volodymyrk

One “idea - execution - output” triplet per cell

Import Cell: expected output is no import errors

CMD+SHIFT+P

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Tip 4: each cell should have one logical output

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Tip 5: write tests .. in jupyter notebooks

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https://pypi.python.org/pypi/pytest-ipynb

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Tip 6: ..to the cloud

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@KNerush @Volodymyrk

Code Smells .. in ipynb

- Cells can’t be executed in order (with runAll and Restart&RunAll)

- Prototype (check ideas) code is mixed with “analysis” code

- Debugging cells

- Copy-paste cells

- Duplicate code (in general)

- Multiple notebooks that re-implement the same function

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@KNerush @Volodymyrk

Tip 7: Run notebook from another notebook!

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analysis.ipynb

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Make Data Product from notebooks!

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@KNerush @Volodymyrk

Summary: How to organise a Jupyter project

1. Notebook should have one Hypothesis-Data-Interpretation loop

2. Make a multi-project utils library

3. Good jupyter notebook reads like a well written prose

4. Each cell should have one and only one output

5. Write tests in notebooks

6. Deploy a shared Jupyter server

7. Try to keep code inside notebooks. Avoid refactoring to modules, if possible.

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