Operators

Operation	Operator	Example	Evaluates to
Addition	+	2 + 2	4
Subtraction	-	4 - 1	3
Multiplication	*	1.5 * 2	3.0
Division	/	5 / 2	2.5
Floor Division	//	5 // 2	2
Modulus (remainder of division)	%	5 % 2	1
Exponent	**	3**3	27

Resulting types

• If any of the operands is a float, result will be a float. Otherwise (both are integer), result is an integer.

• However, there is an exception: result of a division (not floor division) is always a float. Careful with that! (why? we’ll see in a moment)

Operator precedence

• Always be careful with expressions using more than one operator! For example:

a = 3
b = 6
c = a + b * 2
print(c)

• This evaluates as \(a + (b \times 2) = 3 + (6 * 2) = 3 + 12 = 15\)

Python operator precedence order:

1. Parentheses: ()
2. Exponents: **
3. Multiplication, divisions and modulus: * / // %
4. Addition and subtraction: + -
5. Comparisons: <= < >= > == != is (next week)
6. Boolean not (next week)
7. Boolean and (next week)
8. Boolean or (next week)

Operators in strings

• Python also permits using SOME operators with strings. In a metaphorical way…

String Operation	Metaphor	Operator	Example	Evaluates to
Concatenation	Addition	+	"Hey" + " " + "apple"	"Hey apple"
Repetition	Multiplication	*	"na" * 4	"nananana"

• Other operators are not supported. Multiplication of a string with another string is also not supported. Both wouldn’t make so much sense…

Evaluating operations in strings

It is also possible to evaluate an expression coded as a string. For example:

expression = "2 * (4 + 6) / 3 - 5"
result = eval(expression)
print(result)

1.666666666666667