In this Pydon't I talk about Python style and I go over some tools you can use to help you remain within a consistent style.
(If you are new here and have no idea what a Pydon't is, you may want to read the Pydon't Manifesto.)
The overall style of your code can have a great impact on the readability of your code. And code is more often read than written, so you (and others!) have a lot to benefit from you writing well stylised code.
In this Pydon't, you will:
By the way, this week I wrote a shorter and lighter article, as I am still investing lots of time preparing for Euro Python 2021... I hope you still find it useful!
You can now get your free copy of the ebook “Pydon'ts – Write beautiful Python code” on Gumroad to help support the series of “Pydon't” articles 💪.
Humans are creatures of habit. From the fact that the first leg that goes into your trousers is always the same, to the fact that you always start brushing your teeth on the same side.
These habits automate routines that do not require much attention, so that you can spend your precious brain power on other things.
As far as my experience goes, the same can be said about your coding style: if you write with a consistent code style, it becomes easier to read because you already expect a given structure; you are only left with acquiring the information within that structure.
Otherwise, if your style isn't consistent, you have to spend more precious brain power parsing the structure of what you are reading and only then apprehend the information within that structure.
PEP 8 is a document whose purpose is to outline a style guide for those who write Python code. It has plenty of useful recommendations. However, right after the introduction, PEP 8 reads
“A style guide is about consistency. Consistency with this style guide is important. Consistency within a project is more important. Consistency within one module or function is the most important.
However, know when to be inconsistent -- sometimes style guide recommendations just aren't applicable. When in doubt, use your best judgment. Look at other examples and decide what looks best. And don't hesitate to ask!”
This is very important: PEP 8 is a style guide that contains recommendations, not laws or strict rules. And what is more, notice that there is a strong focus on consistency. Using your own (possibly weird) style consistently is better than using no style at all. That's if you are working alone; in a project, it is a good idea to decide on a particular style beforehand.
When I'm teaching Python, I often do some sort of live coding, where I explain things and type examples, that I often ask students to type as well. I have noticed that people that are just starting with Python will often copy the words that I'm typing, but won't respect my whitespace usage.
It is a bit of an exaggeration, but I might type
def f(a, b, x): return a*x + b
and then they will type things like
def f (a,b , x): return a *x+ b
Python is the language where whitespace matters (because Python uses indentation to nest structures), but whitespace turns out to be important in more places than just those.
For example, above, we can see that the misuse of blank spaces
makes the second definition of
f much more hectic and aesthetically unpleasant.
And if there is one thing we know, is that elegance matters.
If you skim through PEP 8 you will find that most recommendations there are about whitespace. Number of empty lines around functions, classes, methods; whitespace around operators and keywords; whitespace before/after commas; etc. Take a look at PEP 8 and gradually try to incorporate some recommendations into your coding.
For example, PEP 8 suggests that you use whitespace to help the reader parse the priority of mathematical operations in an expression. Above, I wrote
return a*x + b
+ with blanks,
to indicate that the
a*x (notice the lack of blanks around
*) has higher priority.
Of course, the number of blank spaces I use doesn't alter the order of operations,
but it helps you see the order of things.
And the cool thing is that the more used to writing like this you are, the more helpful it becomes!
Again, my suggestion is that you take a look at PEP 8 and pick a couple of recommendations you enjoy and try incorporating those into your coding. When those sink in, add a couple more. And just roll with that. Easier than trying to change everything all at once.
On a happier note, there are many tools you can use that help you format your code and keep it neat and tidy.
A class of tools that you can use is what are known as (auto-)formatters,
black is a prime example (see their repo here).
black take your code and reformat it so that it fits
within the style that the tool supports/you configure.
For example, let me create the file
my_f.py and paste this code in there:
# In my_f.py def f (a,b , x): return a *x+ b
Now let me run
black on that file:
> python -m black my_f.py reformatted my_f.py All done! ✨ 🍰 ✨ 1 file reformatted.
Now, I open my file and this is what is inside:
# In my_f.py def f(a, b, x): return a * x + b
As we can see,
black took my code and just reformatted it to the style
black adheres to.
black's style is fairly similar to PEP 8's style and
black is a great
tool if you just want to have something automatically helping you reformat your code,
so that you don't have to think too much about it.
black is as easy to install as any other Python module:
python -m pip install black
There are many tools like
black out there;
another common option is
pycodestyle checks if your style is similar to what PEP 8 recommends.
pycodestyle used to be called
but was renamed so that people understand that:
pycodestyledoesn't match PEP 8's recommendations 100%.
Let me modify the file
my_f.py to the following:
# In my_f.py import os, time def f(a, b, x): return a * x + b
If I run
pycodestyle, this is what I get as output:
> python -m pycodestyle my_f.py my_f.py:2:10: E401 multiple imports on one line my_f.py:3:1: E302 expected 2 blank lines, found 0
We can see that
pycodestyle complained about a couple of things:
import time; and
A big difference between
pycodestyle is that
does reformat your code, whereas
pycodestyle just complains.
pycodestyle is just a matter of typing
python -m pip install pycodestyle
For both tools, and for most of the similar tools out there, you can configure them to ignore types of errors, or ignore sections of your code, etc. Just go read their documentation!
(Auto-)Formatters are helpful, but there are other tools out there that have even more potential: linters.
Linters are tools that analyse your code and help you find things like
These tools can be incredibly helpful, for example, to manage all the imports in a big project. I often find myself importing some modules and using them. Later, I refactor my code, and I stop needing those imports. When I do that, I always forget to check if the imports are still needed or no longer relevant. Linters can, for example, flag unused imports.
An example of a linter is
flake8 (you can find it here).
If I use
flake8 on my
my_f.py file, here is what I get:
> python -m flake8 my_f.py my_f.py:2:1: F401 'os' imported but unused my_f.py:2:1: F401 'time' imported but unused my_f.py:2:10: E401 multiple imports on one line my_f.py:3:1: E302 expected 2 blank lines, found 0
You can see that now
flake8 is complaining about the fact that I am importing things that I don't use at all!
Not only that, but the two bottom lines are identical to
pycodestyle's output above...
And that's because
pycodestyle within itself.
You can install
python -m pip install flake8
Another fairly common alternative for a linter is
Running it on the same
my_f.py file, I get some more warnings:
> python -m pylint my_f.py ************* Module my_f my_f.py:1:0: C0114: Missing module docstring (missing-module-docstring) my_f.py:2:0: C0410: Multiple imports on one line (os, time) (multiple-imports) my_f.py:3:0: C0103: Function name "f" doesn't conform to snake_case naming style (invalid-name) my_f.py:3:0: C0103: Argument name "a" doesn't conform to snake_case naming style (invalid-name) my_f.py:3:0: C0103: Argument name "b" doesn't conform to snake_case naming style (invalid-name) my_f.py:3:0: C0103: Argument name "x" doesn't conform to snake_case naming style (invalid-name) my_f.py:3:0: C0116: Missing function or method docstring (missing-function-docstring) my_f.py:2:0: W0611: Unused import os (unused-import) my_f.py:2:0: W0611: Unused import time (unused-import) ------------------------------------- Your code has been rated at -20.00/10
We can see that
pylint was more unforgiving,
complaining about the fact that I did not include docstrings
and complaining about my 1-letter names.
This might be something you appreciate!
I reckon personal taste plays a big role in picking these tools.
pylint can be done through
python -m pip install pylint
As far as these tools are concerned, I suggest you pick something that is fairly consensual for your personal projects, so that it doesn't hurt you too much when you contribute to other projects. For open source projects, you will often be asked to follow a given style, and there may or may not be tools that help you reformat your code to follow that style.
This article was not supposed to be a thorough review of all the possibilities there are out there, I only touched upon a couple of popular alternatives, so that might be a decent indicator of things that are consensual.
By the way, many IDEs these days have integrated support for these linters, making it even easier to harness their helpful suggestions.
Here's the main takeaway of this Pydon't, for you, on a silver platter:
“Pay attention to the style with which you write code and pick a suite of tools to help you if you want/need.”
This Pydon't showed you that:
pycodestylecan help you fix the style of your code; and
pylintcan give further insights into some types of errors/bugs/problems your programs might have.
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black- The Uncompromising Code Formatter, https://github.com/psf/black [last accessed 20-07-2021];
pycodestyle, https://pycodestyle.pycqa.org/en/latest/intro.html [last accessed 20-07-2021];
pydocstyle, http://www.pydocstyle.org/en/stable/ [last accessed 20-07-2021];
flake8, https://flake8.pycqa.org/en/latest/index.html [last accessed 20-07-2021];
pylint, https://www.pylint.org/ [last accessed 20-07-2021];