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Python: Priority

Let us imagine that we need to calculate such an expression: 2 + 2 * 2. That's exactly what we'll write down:

print(2 + 2 * 2)  # => 6

In school mathematics there is a concept of "operation priority". The priority determines in what order the operations should be performed. Multiplication and division have a higher priority than addition and subtraction, and the priority of exponentiation is higher than all other arithmetic operations. For example: 2 ** 3 * 2 will be calculated in 16.

But often the calculations must take place in an order different from the standard priority. Then the priority must be set with parentheses. This was also the case at school, for example: (2 + 2) * 2. Brackets can be placed around any operation. They can fit into each other as many times as you like. Here are examples:

print(3 ** (4 - 2))  # => 9
print(7 * 3 + (4 / 2) - (8 + (2 - 1)))  # => 14

The main thing is to observe pairing - to close brackets in the correct order. This is often the cause of errors not only for beginners, but for experienced programmers as well. For convenience, put the opening and closing parentheses at once, and then write the inner part. The editor on our site (and most other code editors) do this automatically: you write (, and the editor immediately adds ). This also applies to other paired characters, such as quotation marks. We'll talk about them in future lessons.

Sometimes an expression is hard to perceive visually. Then you can place brackets without affecting the priority:

# Was
print(8 / 2 + 5 - -3 / 2)  # => 10.5

# Became
print(((8 / 2) + 5) - (-3 / 2))  # => 10.5

The important thing to remember is that code is written for people. People will read the code and machines will only execute it. For machines the code is correct or incorrect. There is no "more" understandable or "less" understandable code for them.


The calculation is given 70 * 3 + 4 / 8 + 2.

Place parentheses so that both additions (3 + 4) и (8 + 2) were calculated in the first place. Print the result on the screen.

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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