Alexis Kestler
The Zen of Python is a collection of 19 software principles that serve as guiding philosophies for programming in Python. These principles, written by Python‘s creator Guido van Rossum, first appeared in the Python source code in the early 1990s.
The Zen of Python emphasizes writing code that is beautiful, explicit, simple, readable, and practical. Following these principles can help you become a better Python programmer by teaching you how to write idiomatic, maintainable, and Pythonic code.
In this comprehensive guide, we‘ll explore what each principle in the Zen of Python means and how you can apply it when writing Python code.
Overview of the Zen of Python
Let‘s first take a look at the full 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!These 19 aphorisms make up the guiding principles for idiomatic Python code. Some of them may seem contradictory at first glance, but most principles build upon and clarify the ones before it.
While the Zen of Python is written poetically, each statement aims to teach an important lesson about writing high-quality Python code. Let‘s now go through each principle in detail to fully understand what it teaches us.
Beautiful is Better Than Ugly
The first principle emphasizes writing beautiful code over ugly code. In other words, strive to write Python code that is elegant, clean, and visually appealing.
For example, consider this function that calculates the squares of numbers from 1 to n:
def get_squares(n):
squares = []
for i in range(1, n+1):
squares.append(i*i)
return squaresThis works, but it is not very beautiful Python code. We can rewrite it in a more elegant way using a list comprehension:
def get_squares(n):
return [i*i for i in range(1, n+1)]The second implementation is more Pythonic and achieves the same result with less code. Always aim to write code like this that leverages Python‘s capabilities for beauty and expressiveness.
Explicit is Better Than Implicit
This principle advises us to be explicit with our code rather than implicit. Make sure the behavior is clearly defined and minimize ambiguity.
For example, when importing modules or functions, always import them explicitly rather than relying on a wildcard import:
# Not ideal
from module import *
# Better
from module import function1, function2Explicit imports make it clear where each component comes from. They prevent name collisions and improve readability.
You should also avoid relying on default parameter values or mutable default parameters since that can introduce unwanted implicit behavior:
# Not ideal
def concatenate(a, b, separator=[‘ ‘]):
return a + separator[0] + b
# Better
def concatenate(a, b, separator=‘ ‘):
return a + separator + bThe second version explicitly passes the separator making the behavior more clear.
Simple is Better Than Complex
Prefer simple and straightforward solutions over complex ones. When possible, avoid over-engineering a piece of code.
For example, you can use a simple list comprehension to square numbers:
[x*x for x in range(10)] Instead of a more complex recursive function:
def square(nums):
if not nums:
return []
return [nums[0]**2] + square(nums[1:])Aim for the most simple and readable approach when writing Python code.
Complex is Better Than Complicated
This principle seems contradictory to the previous one at first. However, it makes an important distinction between complexity and complication.
While we are advised to avoid unnecessary complexity, some solutions require a certain degree of complexity. When needed, complex code is preferable over complicated code.
Complex code is manageable and organized. Complicated code is messy and all over the place.
For example, a machine learning model requires some complex logic and analysis. But if the code implementing it is well-structured and modular, then the complexity is warranted.
However, you should avoid ad-hoc complicated code with no consistent logic or structure even for complex problems. Favor necessary complexity over tangled complication.
Flat is Better Than Nested
Deeply nested code is more difficult to understand than flat code. When possible, avoid excessive nesting by keeping code shallow.
For example:
# Flat is better
for x in range(100):
if x % 2 == 0:
print(x)
# Nested is harder to read
for x in range(100):
if x % 2 == 0:
print(x)
else:
if x % 3 == 0:
print(x)The nested if statements in the second example make the code more difficult to parse. Favor flat code when you can.
Sparse is Better Than Dense
Don‘t overuse advanced Python features just because you can. Readability suffers when code is too dense.
For example, you can implement a dictionary with multiple nested list comprehensions:
pairs = {(x, y) for x in range(10) for y in range(10)}But it is harder to read than a simple for loop:
pairs = {}
for x in range(10):
for y in range(10):
pairs[(x, y)] = 0Use Pythonic constructs like comprehensions judiciously. Don‘t sacrifice readability for terse code.
Readability Counts
Code should be written for humans first and computers second. Always ensure your code is readable and easy to understand.
Ways to improve readability:
- Use descriptive variable names
- Break code into functions and classes when it gets long
- Add comments to explain complex logic or unintuitive code
- Use whitespace and newlines for visual separation
Readability directly impacts maintainability. The easier code is to read, the easier it is to maintain and modify when needed.
Special Cases Aren‘t Special Enough to Break the Rules
Try to follow Python‘s standard conventions and idioms. Don‘t violate them for niche use cases unless absolutely necessary.
For example, Python utilizes underscores to denote private module/class members. You should avoid accessor functions in favor of simply accessing the variable directly even if it breaks encapsulation:
# Unpythonic
class Point:
def __init__(self, x, y):
self._x = x
self._y = y
def get_x(self):
return self._x
# Pythonic
class Point:
def __init__(self, x, y):
self._x = x
self._y = y
# Direct access
p = Point(5, 7)
x = p._x Adhering to Python‘s conventions leads to more idiomatic and maintainable code.
Although Practicality Beats Purity
While the previous principle recommends following conventions, this one argues for pragmatism over purity at times.
If violating a convention meaningfully improves code quality, then it may be justified. For example, naming a variable _x instead of x to avoid clashes with a keyword may improve readability despite violating conventions about underscores.
Pragmatic thinking focused on practical code quality trumps blind conformity to principles. Use good judgment here!
Errors Should Never Pass Silently
Make sure to handle errors rather than ignore them. Don‘t suppress or silence exceptions without handling them properly.
For example, simply silencing exceptions allows bugs to go unnoticed:
# Bad
try:
dangerous_call()
except Exception:
pass
# Good
try:
dangerous_call()
except DangerousException:
log("Warning: Encountered DangerousException")The second example handles the specific exception properly. This results in robust programs that fail loudly on errors.
Unless Explicitly Silenced
This principle clarifies the previous one – it is fine to silence errors if you do so intentionally for good reason.
For example, you may want to ignore connection errors temporarily in order to retry the connection:
retries = 3
while retries > 0:
try:
connect_to_server()
break
except ConnectionRefusedError:
retries -= 1Here we explicitly silence the connection error to implement retry logic. Intentional silencing like this is okay.
In the Face of Ambiguity, Refuse the Temptation to Guess
When something is ambiguous, avoid guessing. Take the time to properly understand the expected behavior.
For example, given:
values = [1,2,3]
print(values[True]) It may be unclear what would happen here. Rather than guess, run the code and let the resulting exception guide you.
Let the Python interpreter tell you the answer when unsure! Don‘t introduce guesses or assumptions.
There Should Be One–and Preferably Only One–Obvious Way to Do It
For a given task, there should be one obvious and idiomatic way to accomplish it in Python.
For example, to iterate over a dictionary, you should use the keys(), values(), or items() methods rather than directly accessing the keys and values yourself:
# Unpythonic
for key in my_dict:
value = my_dict[key]
# Pythonic
for key, value in my_dict.items():
passLeveraging built-ins leads to more idiomatic code than manual approaches. Use the "one right way" when possible.
Although That Way May Not Be Obvious at First Unless You‘re Dutch
This pokes fun at Python creator Guido van Rossum‘s Dutch heritage. While Python aims to provide obvious solutions to problems, they may not be obvious to all programmers at first glance.
It often requires experience with Python and computer science in general to recognize the most idiomatic approaches. Don‘t expect them to be obvious immediately – keep learning!
Now is Better Than Never
It‘s easy to procrastinate writing perfect code indefinitely. But working code today is better than perfect code tomorrow.
Don‘t let striving for perfection prevent progress. Get something working now, then iterate on it.
For example, when starting a new project:
# Perfect? No.
# Runs successfully? Yes!
class User:
pass
user = User()
print(user)This trivial example will evolve over time. But get the ball rolling rather than waiting!
Although Never is Often Better Than Right Now
This principle seems contradictory but offers wisdom. Rushing into code can cause problems.
Pausing to think through all requirements before diving into code often produces better initial results. As the Zen notes, "never is often better than right now".
So take the time to design solutions before implementing them. Rushing leads to disorganized code that requires extensive refactoring.
Find the right balance between proper planning and continuous progress. Move steadily rather than rushing or procrastinating.
If the Implementation Is Hard to Explain, It‘s a Bad Idea
Beware of overly complex code that is difficult to explain. This signals that simplification may be needed.
Refactor algorithms and designs that you cannot easily describe to others. Simplify complicated code into easy to explain solutions.
Clear and simple explanations are a sign of good code. If an explanation is confusing, the code likely will be as well.
If the Implementation Is Easy to Explain, It May Be a Good Idea
The counterpart to the previous principle – implementations that are simple to explain may be on the right track.
When you find an algorithm or approach that you can describe in plainly, stick with it! Clear explanations lead to maintainable code.
Simple explanations also make it easier for others to learn and modify the code later on. Seek easily explained solutions.
Namespaces are One Honking Great Idea — Let‘s Do More of Those!
Python‘s namespace feature helps avoid naming collisions by scoping names. This is invaluable in large programs with many moving parts.
Leverage Python namespaces by:
- Using modules for logical grouping of code
- Defining functions and classes to create local scopes
- Using descriptive variable names to avoid clashes
Conclusion
The Zen of Python contains wisdom that guides programmers towards writing beautiful, idiomatic code. While some principles seem contradictory, they aim to teach important lessons about achieving simplicity, readability, and practicality in Python.
By teaching you how to write Pythonic code, the Zen of Python will naturally make you a stronger Python programmer. Some principles will resonate with you more than others depending on your experience level.
I recommend periodically reviewing the Zen of Python – especially after gaining more experience with Python. The principles will continue to provide valuable insights as you advance and take on more complex programs.
Always view code through the lens of these principles. Strive for beautiful, explicit, simple, practical Python code that leverages all the clarity and power the language provides.
The Zen of Python embodies a treasure trove of useful advice. Follow its wisdom and you will notice steady improvements in your abilities to write idiomatic, well-structured Python code. Master these principles and approaches, and you will master Python itself.
