The Zen of Python is a collection of guiding principles for writing computer programs in the Python language. It was written by Tim Peters, a core Python developer, and was first introduced in 2004 as PEP 20 (Python Enhancement Proposal). These principles are meant to encourage clarity, simplicity, and readability in Python code.

You can view the Zen of Python in Python itself by running:

import this

The Zen of Python, by Tim Peters

  1. Beautiful is better than ugly.
  2. Explicit is better than implicit.
  3. Simple is better than complex.
  4. Complex is better than complicated.
  5. Flat is better than nested.
  6. Sparse is better than dense.
  7. Readability counts.
  8. Special cases aren't special enough to break the rules.
  9. Although practicality beats purity.
  10. Errors should never pass silently.
  11. Unless explicitly silenced.
  12. In the face of ambiguity, refuse the temptation to guess.
  13. There should be one-- and preferably only one --obvious way to do it.
  14. Although that way may not be obvious at first unless you're Dutch.
  15. Now is better than never.
  16. Although never is often better than right now.
  17. If the implementation is hard to explain, it's a bad idea.
  18. If the implementation is easy to explain, it may be a good idea.
  19. Namespaces are one honking great idea -- let's do more of those!
Clearly a job for Guido alone – although I doubt it’s one he’ll take on (fwiw, I wish he would too!). Here’s the outline he would start from, though <wink>:

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!

There you go: 20 Pythonic Fec^H^H^HTheses on the nose, counting the one I’m leaving for Guido to fill in. If the answer to any Python design issue isn’t obvious after reading those – well, I just give up <wink>.

NOTE: Mysteriously, only 19 of the guidelines are written down. Guido van Rosum reportedly said that the missing 20th aphorism is "some bizarre Tim Peters in-joke."

Detailed Breakdown of Each Principle

1. Beautiful is better than ugly.

Programmers often write code quickly without concern for readability. While code doesn't have to be readable, the code of the Python language itself must be thought out, consistent, and a joy to use. Of course, not every script needs to be beautiful, and beauty is subjective, but much of Python's popularity is a result of being so easy to work with.

  • Code should be aesthetically pleasing.
  • Clean, well-structured code is easier to understand and maintain.
  • Avoid messy, disorganized, and unreadable code.

2. Explicit is better than implicit.

"This aphorism is self-explanatory," that would be a terrible explanation for any aphorism. Similarly, it's better for code to be verbose and explicit. You should avoid hiding code's functionality behind obscure language features that require familiarity to fully understand.

  • Code should be clear in its purpose.
  • Avoid "magic" that makes it hard to understand how something works.

3. Simple is better than complex.

4. Complex is better than complicated.

These two aphorisms remind us that building anything can be done using simple or complex techniques. With a simple problem, such as building a birdhouse, a simple solution is better. Building a diesel train engine, on the other hand, is a complex problem that requires complex techniques. Even if you could technically make a diesel train engine using birdhouse techniques, you probably would end up with a complicated, Rube Goldberg arrangement of birdhouse parts that wouldn't be an ideal solution. Prefer simplicity to complexity, but know the limits of simplicity.

  • Keep your solutions as simple as possible.
  • Simplicity makes code easier to debug and maintain.
  • Sometimes, complexity is necessary, but it should not be overcomplicated.
  • A well-structured complex solution is better than an unnecessarily convoluted one.

5. Flat is better than nested.

Programmers love to organize things into categories, especially categories that contain subcategories which contain other sub-subcategories. These hierarchies often don't add organization so much as they add bureaucracy. It's okay to have code in just one top-layer module or class instead of split up across multiple submodules or subclasses. If you make packages and modules that require code like import spam.eggs.bacon.ham.foo.bar, then you're making your code too complicated.

  • Avoid deep nesting as it makes code harder to read.

6. Sparse is better than dense.

Programmers often like to cram as much functionality into as little code as possible. While code like this may impress their friends, it'll infuriate their coworkers who have to try to understand it. Code that is spread out over multiple lines is often easier to read than dense one-liners.

  • Use whitespace and line breaks to improve readability.
  • Avoid writing code in a compressed, unreadable manner.

7. Readability counts.

While strcmp() may obviously mean the "string compare" function to someone who has been programming in C since the 1970s, modern computers have enough memory to write out the full function name. Don't drop vowels from your names or write overly terse code. Code is read more often than it's written, so explicit, readable code is more important than terse, undocumented code.

  • Code is read more often than it is written.
  • Write code that is easy to understand.

8. Special cases aren't special enough to break the rules.

9. Although practicality beats purity.

These two aphorisms, which come as a set, contradict each other. Programming is full of "best practices" that programmers should strive for in their code. Skirting these practices for a quick hack may be tempting, but can lead to a rat's nest of inconsistent, unreadable code. However, bending over backwards to adhere to rules can result in highly-abstract, unreadable code. The Java programming language's attempt to fit all code to its object-oriented paradigm often results in lots of boilerplate code for even the smallest program. Walking the line between these two aphorisms becomes easier with experience. And in time, you'll not only learn the rules, but also learn when to break them.

  • Stick to consistent patterns rather than making exceptions.
  • Avoid hacks that work for specific cases but break general principles.
  • Sometimes, practical solutions are preferable to perfect ones.
  • Follow best practices but be flexible when necessary.

10. Errors should never pass silently.

11. Unless explicitly silenced.

Just because programmers often ignore error messages doesn't mean the program should stop emitting them. Silent errors can happen when functions return error codes or None instead of raising exceptions. These two aphorisms tell us that it's better for a program to fail fast and crash than to silence the error and continue running the program. The bugs that inevitably happen later on will be harder to debug since they are far removed from the original cause. Though you can always choose to explicitly ignore the errors your programs cause, just be sure you are making the conscious choice to do so.

  • Errors should be handled properly.
  • Silently ignoring errors can lead to unexpected behavior.
  • If you must silence an error, do it explicitly.

12. In the face of ambiguity, refuse the temptation to guess.

Computers have made humans superstitious: To exorcise the demons in our computers we perform the sacred ritual of turning them off and then on. Supposedly this will fix any mysterious problem. However, computers are not magic. If your code isn't working, there is a reason and only careful, critical thinking will solve it. Refuse the temptation to blindly try solutions until something seems to work; often you have merely masked the problem rather than solved it.

  • If something is unclear, clarify it rather than assuming.
  • Write code that removes ambiguity.

13. There should be one-- and preferably only one --obvious way to do it.

This is a broadside against the Perl programming language's motto, "There's more than one way to do it!" It turns out that having three or four different ways to write code that does the same thing is a double-edged sword: you have flexibility in how you write code, but now you have to learn every possible way it could have been written in order to read it. This flexibility isn't worth the 3x or 4x effort needed to learn a programming language.

  • Python values having a clear, straightforward way to accomplish tasks.
  • This principle contrasts with Perl's "There's more than one way to do it."

14. Although that way may not be obvious at first unless you're Dutch.

This line is a joke. Guido van Rossum, the creator and BDFL (Benevolent Dictator for Life) of Python, is Dutch. However, not even this aphorism prevented Python from incorporating three different ways of formatting strings.

  • A humorous reference to Guido van Rossum, Python's Dutch creator.
  • Some Pythonic ways may take time to learn.

15. Now is better than never.

16. Although never is often better than right now.

These two aphorisms tell us that code that hangs or gets caught in infinite loops is obviously worse than code that doesn't. However, it's almost certainly better to wait for your program to finish than to have it finish too early with incorrect results.

  • Don't overthink or overengineer - deliver solutions in a reasonable timeframe.
  • Avoid rushing into solutions that may cause long-term problems.
  • Think things through before implementation.

17. If the implementation is hard to explain, it's a bad idea.

18. If the implementation is easy to explain, it may be a good idea.

Python strives to make the programmer's job easier rather than accommodate the computer so a program runs faster. And programs need to be understandable not just by the programmer who wrote it, but also by other programmers who maintain the code. These two aphorisms remind us that if "high-performance" code is so complicated as to be impossible for programmers to understand and debug, then it's bad code. But alas, just because it's easy to explain a program's code to someone else doesn't mean it isn't bad code. Programming is hard.

  • Code should be understandable to others.
  • Simple and clear solutions are often the best.

19. Namespaces are one honking great idea -- let's do more of those!

Namespaces (and also global and local scopes) are key for preventing names in one module or scope from conflicting with names in another. But also remember that flat is better than nested: As great as they are, namespaces should be made only to prevent naming conflicts, and not to add needless categorization.

  • Encourages the use of namespaces to avoid conflicts.

The Zen of Python is not a strict set of rules but a philosophy that encourages clarity, simplicity, and readability in Python programming. By following these principles, developers can write better, more maintainable Python code.