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Python: Data types

There are different ways to represent data in programs. There are strings - sets of characters in quotes like "Hello, World!". There are integers - for example, 7, -198, 0. These are two different categories of information - two different types of data. The multiplication operation makes sense for the “integers” category, but not for the “strings” category: it makes no sense to multiply the word “mom” by the word “notepad”.

The data type determines what can be done with the elements of a particular set of information. In this lesson we'll learn about data types and how typing works in Python.

The programming language recognizes data types, so Python won't let us multiply a string by another string - you can't multiply text by text. You can multiply an integer by another integer. The existence of types and these restrictions in the language protects programs from accidental errors.

Unlike strings, numbers don't need to be wrapped in quotes. To print the number 5, all you have to do is write:

print(5)  # => 5

The number 5 and the string '5' are completely different things, although the output given by print() for this data is identical. Whole numbers (1, 34, -19, etc.) and rational numbers (1.3, 1.0, 14.324, etc.) are two separate types of data. This division is due to the peculiarities of how computers are set up. There are other types, which we'll get to know later.

Here's another example, but with a rational number:

print(10.234)  # => 10.234

The data types “string”, “integer” and “rational number” are primitive types, i.e., they're built into the Python language itself. Some composite types are also built into the language, but for now, we'll only be working with the primitive ones. Programmers can also create their own data types.

In English, strings in programming are called strings, and lines in text files are called lines. For example, in the code above there is a line, but no strings. In Russian there can sometimes be confusion, so in all the lessons we will say string to indicate the data type "string", and string to indicate lines in the code (lines) in the files.


Display the number -0.304.

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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  • Data type a set of data in a code (a kind of information). A type determines what you can do with the elements of a particular set. For example, integers, rational numbers, and strings are different types of data.

  • Primitive data types simple types built into the programming language itself.

  • String a data type that describes a character set (in other words, text) such as 'text' or "text".

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