# Python tutorial #4 : arithmetic operations

For Terminal

`python`

How to use IDLE

## Arithmetic operations cheat sheet

``````x + y    addition
x - y    subtraction
x * y    multiplication
x / y    division
x // y   Division (rounded down to the nearest whole number)
x % y    Surplus
+x       As it is
x ** y   Exponentiation
``````

## python arithmetic operations priority

``````↑ High priority

(), [], {},             list / tuple / dict
await x                 Await
**                      Exponentiation
+x, -x, ~x              Positive / Negative / Bitwise
*, @, /, //, %          Multiplication / matrix multiplication / division / truncation division / remainder
<<, >>                  Shift operation
&                       Bitwise AND
^                       Bitwise XOR
|                       Bitwise OR
in, not in, is, is not, Comparison including affiliation and identity tests
<, <=, >, >=, !=, ==    Comparison including affiliation and identity tests
not x                   Boolean operation NOT
and                     Boolean operation AND
or                      Boolean operation OR
if -- else              Conditional expression
lambda                  Lambda expression

↓ Low priority
``````

`1 + 2 * 3` = 7

`1 + 3 / 7` = 0.4285714285714286

`1 + 8 // 2` = 5

`1 + 2` = 3

`1.23 + 2.6` = 3.83

## Subtraction -Operator

Unable to do subtraction in python

`2 - 5` = -3

This is the code 2 + -5, so if you want to do a subtraction, you have to write it at the end of the column.

`1 - 6 / 2` = -2.0

error

`6 / 2 - 1` = 2.0

correct

## Multiplication *operator

`2 * 3` = 6

`6.5 * 20.5` = 133.25

## Division /Operator

`6 / 2` = 3.0

`3 / 7` = 0.42857142857142855

`25 / 4` = 6.25

### Handling of decimal point

`3 / 7` = 0.42857142857142855

Output in python

0.428571428571428571

`3 / 11` = 0.2727272727272727

Output in python

0.27272727272727272

Division displays 17 digits after the decimal point. Numbers longer than 17 digits are not displayed even if they exist

### arithmetic operations Rounding

``````1 / 9 = 0.1111111111111111
2 / 9 = 0.2222222222222222
3 / 9 = 0.3333333333333333
4 / 9 = 0.4444444444444444
5 / 9 = 0.5555555555555556
6 / 9 = 0.6666666666666666
7 / 9 = 0.7777777777777778
8 / 9 = 0.8888888888888888
9 / 9 = 1.0
``````

・For some reason, indivisible numbers between 5 and 7 are rounded up to the nearest whole number.
・Indivisible numbers in 0.999 ... are displayed as approximately 1.0

## Integer part of division Integer division //Operator omitted

### Truncate

When performing division, it is recommended to use `//`, which is rounded down to the nearest whole number, unless accurate calculation is required.

Reason

・Numbers (ints) that have a decimal point are called float types, which complicates the code. ・Execution speed takes about 10 times (slows down) ・Increased probability of human error

`25 // 4` = 6

### Handling of decimal points in `//`

``````1 // 9 = 0
2 // 9 = 0
3 // 9 = 0
4 // 9 = 0
5 // 9 = 0
6 // 9 = 0
7 // 9 = 0
8 // 9 = 0
9 // 9 = 1
``````

### Division remainder remainder mod %operator Percentage

% Is often used mainly when using machine learning. Let's take the gross profit amount and the gross profit rate as an example.

・Cost
`cost = 14`

・Selling price
`sales = 85`

・Gross profit
`gp = (sales - cost)`

`print('{:,}'.format(gp))`

71

・Gross profit margin
`gpr = gp / sales`

`print('{:%}'.format(gpr))`

83.529412%

You can see that the gross margin is about 83%

## Exponentiation **Operator

`4 ** 4` = `4 * 4 * 4 * 4` = 256

`5 ** 3` = `5 * 5 * 5` = 125

Cubic centimeters Useful when calculating square centimeters Thank you for watching until the end. I'm glad if you can use it as a reference.

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