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Python Software Engineering Best Practices Cheat Sheet by

Like any other language or tool, Python has some best practices to follow before, during, and after the process of writing your code. These make the code readable and create a standard across the industry. Other developers working on the project should be able to read and understand your code.

Clean and Modular Code

Production Code
software running on production servers to handle live users and data of the intended audience.
Production Quality Code
code that meets expect­ations in reliab­ility, efficiency, etc., for produc­tion.
Clean Code
readable, simple, and concise.
Modular Code
logically broken up into functions and modules.
a file. Modules allow code to be reused by encaps­ulating them into files that can be imported into other files.
Making your code Modular makes it easier to
Reuse your code
Write less code
Read your code
Collab­orate on code
Refact­­oring Code
restru­cturing your code to improve its internal structure, without changing its external functi­ona­lity. This gives you a chance to clean and modularize your program after you've got it workin­g.p­rogram after you've got it working.

Writing Clean Code: Meaningful Names

Be descri­ptive and imply type
E.g. for booleans, you can prefix with
to make it clear it is a condition. You can also use part of speech to imply types, like verbs for functions and nouns for variables.
Be consistent but clearly differ­entiate
is easier to differ­entiate than
Avoid abbrev­iations and especially single letters
(Excep­tion: counters and common math variables) Choosing when these exceptions can be made can be determined based on the audience for your code. If you work with other data scient­ists, certain variables may be common knowledge. While if you work with full stack engineers, it might be necessary to provide more descri­ptive names in these cases as well.
Long names != descri­ptive names
You should be descri­ptive, but only with relevant inform­ation. E.g. good functions names describe what they do well without including details about implem­ent­ation or highly specific uses.
Try testing how effective your names are by asking a fellow programmer to guess the purpose of a function or variable based on its name, without looking at your code. Coming up with meaningful names often requires effort to get right.

Writing Clean Code: Nice Whitespace

Organize your code with consistent indent­ation
the standard is to use 4 spaces for each indent. You can make this a default in your text editor.
Separate sections with blank lines to keep your code well organized and readable.
Try to limit your lines to around 79 charac­ters, which is the guideline given in the PEP 8 style guide.
In many good text editors, there is a setting to display a subtle line that indicates where the 79 character limit is.
For more guidel­ines, check out the code layout section of PEP 8

Writing Modular Code

DRY (Don't Repeat Yourself)
Don't repeat yourself! Modula­riz­ation allows you to reuse parts of your code. Generalize and consol­idate repeated code in functions or loops.
Abstract out logic to improve readab­ility
Abstra­cting out code into a function not only makes it less repeti­tive, but also improves readab­ility with descri­ptive function names. Although your code can become more readable when you abstract out logic into functions, it is possible to over-e­ngineer this and have way too many modules, so use your judgement.
Minimize the number of entities (funct­ions, classes, modules, etc.)
There are tradeoffs to having function calls instead of inline logic. If you have broken up your code into an unnece­ssary amount of functions and modules, you'll have to jump around everywhere if you want to view the implem­ent­ation details for something that may be too small to be worth it. Creating more modules doesn't necess­arily result in effective modula­riz­ation.
Functions should do one thing
Each function you write should be focused on doing one thing. If a function is doing multiple things, it becomes more difficult to generalize and reuse. Generally, if there's an "­and­" in your function name, consider refact­oring.
Arbitrary variable names can be more effective in certain functions
Arbitrary variable names in general functions can actually make the code more readable.
Try to use fewer than three arguments per function
Try to use no more than three arguments when possible. This is not a hard rule and there are times it is more approp­riate to use many parame­ters. But in many cases, it's more effective to use fewer arguments. Remember we are modula­rizing to simplify our code and make it more efficient to work with. If your function has a lot of parame­ters, you may want to rethink how you are splitting this up.

Efficient Code

Execute faster
Take up less space in memory­/st­orage
The project you're working on would determine which of these is more important to optimize for your company or product. When we are performing lots of different transf­orm­ations on large amounts of data, this can make orders of magnitudes of difference in perfor­mance.
E.g. Sets faster than lists in python


additional text or illust­rated inform­ation that comes with or is embedded in the code of software.

Helpful for clarifying complex parts of code, making your code easier to navigate, and quickly conveying how and why different components of your program are used.

Several types of docume­ntation can be added at different levels of your program:
In-line Comments - line level
Docstrings - module and function level
Project Docume­ntation - project level

Use version control

Version control, also known as revision control or source control, is the management of changes to documents, computer programs, large websites, and other collec­tions of inform­ation. Each revision is associated with a timestamp and the person making the change.
The most famous version control system is Git


Testing your code is essential before deploy­ment. It helps you catch errors and faulty conclu­sions before they make any major impact.
Test driven develo­pment
a develo­pment process where you write tests for tasks before you even write the code to implement those tasks.
Unit Test
a type of test that covers a “unit” of code, usually a single function, indepe­ndently from the rest of the program.

Log Messages

Logging is the process of recording messages to describe events that have occurred while running your software.
Be profes­sional and clear
Bad: Hmmm... this isn't working??? 
Bad: idk.... :(
Good: Couldn't parse file.
Be concise and use normal capita­liz­ation
Bad: Start Product Recomm­end­ation Process 
Bad: We have completed the steps necessary and will now proceed with the recomm­end­ation process for the records in our product database.
Good: Generating product recommendations.
Choose the approp­riate level for logging
DEBUG - level you would use for anything that happens in the program.
ERROR - level to record any error that occurs
INFO - level to record all actions that are user-d­riven or system specific, such as regularly scheduled operations
Provide any useful inform­ation
Bad: Failed to read location data
Good: Failed to read location data: store_id 8324971

Code Reviews

Code reviews benefit everyone in a team to promote best progra­mming practices and prepare code for produc­tion.
Questions to Ask Yourself When Conducting a Code Review
Is the code clean and modular?
Can I understand the code easily?
Does it use meaningful names and whitespace?
Is there duplicated code?
Can you provide another layer of abstraction?
Is each function and module necessary?
Is each function or module too long?
Is the code efficient?
Are there loops or other steps we can vectorize?
Can we use better data structures to optimize any steps?
Can we shorten the number of calcul­ations needed for any steps?
Can we use generators or multip­roc­essing to optimize any steps?
Is docume­ntation effective?
Are in-line comments concise and meanin­gful?
Is there complex code that's missing docume­nta­tion?
Do function use effective docstr­ings?
Is the necessary project docume­ntation provided?
Is the code well tested?
Does the code high test coverage?
Do tests check for intere­sting cases?
Are the tests readable?
Can the tests be made more efficient?
Is the logging effective?
Are log messages clear, concise, and profes­sional?
Do they include all relevant and useful inform­ation?
Do they use the approp­riate logging level?

Conducting a Code Review

Use a code linter
This can save you lots of time from code review. Using a Python code linter like pylint can automa­tically check for coding standards and PEP 8 guidelines for you.
Explain issues and make sugges­tions
BAD: Make model evaluation code its own module - too repeti­tive. 
BETTER: Make the model evaluation code its own module. This will simplify to be less repetitive and focus primarily on building models.
GOOD: How about we consider making the model evaluation code its own module? This would simplify to only include code for building models. Organizing these evalua­tions methods into separate functions would also allow us to reuse them with different models without repeating code.
Keep your comments objective
BAD: I wouldn't groupby genre twice like you did here... Just compute it once and use that for your aggreg­ations.  
BAD: You create this groupby dataframe twice here. Just compute it once, save it as groupb­y_genre and then use that to get your average prices and views.
GOOD: Can we group by genre at the beginning of the function and then save that as a groupby object? We could then reference that object to get the average prices and views without computing groupby twice.
Provide code examples


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