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Python: Floating point numbers

In mathematics there are different kinds of numbers, for example, natural numbers are integers from one and up, or rational numbers are numbers with a point, such as 0.5. From the point of view of computers, there is a chasm between these types of numbers. Try answering the simple question of how much would 0.2 + 0.1? Now let's see what Python has to say about it:

0.2 + 0.1 # 0.30000000000000004

The operation of adding two rational numbers suddenly results in an inaccurate calculation. The same result will be given by other programming languages. Such behavior is due to limitations of computing power. The memory capacity, unlike numbers, is finite (an infinite number of numbers requires an infinite amount of memory to store them).

Rational numbers are not lined up in a continuous chain, between 0.1 и 0.2 an infinite set of numbers. Accordingly, a serious problem arises, but how to store rational numbers? This is an interesting question in itself. There are many articles on the Internet devoted to organizing memory in such cases. Moreover, there is a standard which describes how to do this correctly, and an overwhelming number of languages rely on it.

For us, as developers, it is important to understand that operations with floating numbers are inaccurate (this accuracy can be adjusted), which means that when solving problems involving such numbers, it is necessary to resort to special tricks that allow to achieve the necessary accuracy.


Calculate and display the product of two numbers: 0.39 and 0.22

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 🙄

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