Originally published on my blog.

Introduction

In my last article I explained why I decided to no longer use pylint.

In a nutshell, most pylint warning are now caught by other linters, and all that’s left are some warnings.

In an other article I mentioned flake8 briefly, saying that I preferred a simple bash script to drive the execution of the various linters.

I was concerned that flake8 did not include pylint (now I no longer care of course). Also, I did not like the fact that flake8 forces a specific version for all the linters it runs.

Well, I was wrong (again).

flake8 is awesome

First off, I thought flake8 only combined the pyflakes and pycodestyle linters and nothing else ¹. Well, it also includes mccabe by default.

Also, as explained in the FAQ, there are significant advantages in having the versions of the linters frozen this way.

Here are some other features I overlooked:

• You can use the setup.cfg file to configure all the linters flake8 knows about
• The output is consistent for all the linters
• The checks of any linter can be be disabled on any line with just a # noqa comment

A nice surprise

The last time I upgraded pylint, I only got one new warning. It was on a line looking like this:

my_set = set([elem for elem in my_list if some_condition(elem)])

The intent here is to build a unique set from a list of elements that satisfy a given condition.

pylint emitted the following warning:

R1718: Consider using a set comprehension (consider-using-set-comprehension)

Indeed, the code can also be written like this, using a set comprehension instead:

my_set = {elem for elem in my_list if some_condition(elem)}

Advantages:

• The code is shorter
• We no longer build a list (inside the square brackets) just to throw it immediately afterwards
• The interpreter does not have to look up the set() function, so the code is faster

Well, there is already a flake8 plugin called flake8-comprehension that deals with these kind of issues.

In fact, there are a bunch of flake8 plugins available!

Plus, adding a new flake8 plugin is as easy as running pipenv install --dev <plugin name> and nothing else has to change :)

The future is bright

Itamar Turner-Trauring², in the comment section on dev.to gave an interesting example:

# Note: I've taken the liberty of making the code a bit less abstract
def greet(prefix, name):
    print(prefix, name)

greeters = list()
prefixes = ["Hi", "Hello", "Howdy"]
for prefix in prefixes:
    greeters.append(lambda x: greet(prefix, x))

for greeter in greeters:
    greeter("world")

You may think the following code would print:

Hi world
Hello world
Howdy world

but instead it prints:

Howdy world
Howdy world
Howdy world

This has to do with how the closures work in Python, and the bug is indeed caught by pylint:

$ pylint example.py
 W0640: Cell variable `prefix` defined in loop (cell-var-from-loop)

I did not find a flake8 plugin that could catch this bug right away, but I found flake8-bugbear, a plugin to “find likely bugs and design problems”.

The plugin is well-written, well-tested and easy to contribute to.

I’ve already tried porting some pylint warnings to flake8-bugbear and so far it has been much easier than I thought. ³

Therefore, next time I find a bug that could have been caught by inspecting the AST (which is what both flake8-bugbear and pylint do), I know how to write or contribute to a flake8 plugin in order to automatically catch it during CI.

Thus, I can slowly build a complete replacement for pylint, with just the warnings I care about, and without the configuration issues and false positives.

Bright future indeed!

Thanks for reading this far :)

I'd love to hear what you have to say, so please feel free to leave a comment below, or check out my contact page for more ways to get in touch with me.

1. The name of the project is somewhat misleading.  ↩

2. If you haven’t already, you should definitively check his blog and subscribe to the Software Clown mailing list. ↩

3. Note that the pull request was actually not merged. In reality, I started by blindly adding a new check in flake8 before taking a look at the whole list of flake8 plugins. The pull request got closed because it turned out the check I added was already in the flake8-comprehensions plugin. Sometimes you have to lie to make a better story … ↩