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Python: Linter

We have already learned how to write simple programs, so we can talk a little bit about how to write them correctly.

The code needs to be written in a certain way so that it is understandable and easy to maintain. There are special sets of rules that describe different aspects of writing code - they are called coding standards. The standard in Python is one - PEP8. It answers practically all the questions about how to design this or that part of the code. This document has all the rules you need to follow. We advise newcomers to get in the habit of looking at the PEP8 standard and writing code according to it.

Today you don't need to remember all the rules from the standard because there are special programs that check the code automatically and report violations. Such programs are called linters. They check the code for standards compliance. In Python there are quite a few of them, and the most popular one is — flake8.

Take a look at an example:

result = 1+ 3

Linter will swear for breaking the rule: E225 missing whitespace around operator. By standard, the + operator must always be separated by spaces from the operands.

Above we saw the rule E225 — is one of a large number of rules. Other rules describe indents, names, brackets, mathematical operations, line lengths, and a host of other aspects. Each individual rule seems unimportant and shallow, but together they form the basis of good code. A list of all the flake8 rules is available on a documentation page.

You are already familiar with the linter because the Hexlet platform uses it to check your code in hands-on assignments. Soon you will start using it outside of Hexlet as well, when you implement training projects. You'll set up the linter, and it will check your code already in real development and tell you about irregularities.


Print the result of the following calculation: "the difference between five squared and the product of three and seven". Write the code so that each operator is separated from the operands by spaces.

The exercise doesn't pass checking. What to do? 😶

If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:

  • Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

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