PYTHON BASICS
Python Basics: Arithmetic Operations
Basic math operations
In the last article we learned that data types classify the types of data represented on a computer, and define the operations that can be performed on them. We looked at the four primitive data types: str, int, float, and bool.
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We also used a few int and float operations in our Invoice example. These numeric data types (int and float) possess similar operations called arithmetic operations.
Operations
Addition
Perhaps the most basic arithmetic operation is addition: the sum of two numbers. Like other built-in operators, addition uses infix notation, where the operands are to the left and right of the operator.
2 + 2 = 4 # int + int = int
1 + 0.5 = 0.5 # int + float = float
2.5 + 3.5 = 6.0 # float + float = floatSubtraction
The difference of two numbers.
3 - 2 = 1 # int - int = int
5 - 2.5 = 2.5 # int - float = float
5.5 - 1.5 = 4.0 # float - float = floatMultiplication
The product of two numbers.
2 * 3 = 6 # int * int = int
4 * 2.5 = 10.0 # int * float = float
2.5 * 1.5 = 3.75 # float * float = floatDivision
The quotient of two numbers.
4 / 2 = 2.0 # int / int = float
6 / 2.5 = 2.4 # int / float = float
7.5 / 3 = 2.5 # float / int = float
6.5 / 1.3 = 5.0 # float / float = floatExponentiation
The left operand is raised to the power of the right operand.
3 ** 2 = 9 # int ** int = int
2 ** 1.4 = 2.63 # int ** float = float
3.5 ** 2 = 12.25 # float ** int = float
2.5 ** 1.5 = 3.95 # float ** float = floatModulo
The remainder from the division of two numbers. The modulo operation produces the remainder, not the quotient.
15 % 4 = 3 # int % int = int
6 % 2.5 = 1.0 # int % float = float
15.5 % 4 = 3.5 # float % int = float
8.25 % 3.5 = 1.25 # float % float = floatFloor Division
This operation yields the integer portion of the quotient between two numbers. The decimal is ignored.
5 // 3 = 1 # int // int = int
5 // 3.0 = 1.0 # int // float = float
5.0 // 3 = 1.0 # float // int = float
5.0 // 3.0 = 1.0 # float // float = floatOrder of Operations
When working with numbers, it is often necessary to compose several operations together. For example, the Fahrenheit to Celsius conversion formula,(x-32) * 5/9, makes use of subtraction, multiplication, and division. In Python, all operators have an order that define which expressions are evaluated first. This extends the BEDMAS or PEMDAS rule (Parentheses, Exponents, Multiplication, Division, Addition, and Subtraction).
Operator Name Precedence
----------- ---------------- ------------
() Parenthesis 6
** Exponentiation 5
// Floor Division 4
* Multiplication 3
/ Division 3
% Modulus 2
+ Addition 1
- Subtraction 1Using the precedence rule, the Fahrenheit to Celsius conversion formula is evaluated as follows
Note that the order in which multiplication and division is evaluated does not matter.
Assignment Operators
A common pattern with these arithmetic operators is the reassigning of variables based on previous values. In other words, you might encounter a situation where you need to write x = x + 1, which increments the value of variable x.
Python, along with some other programming languages, provide a shortcut for performing these operations. In the case of x = x+1, we can rewrite it more compactly as x += 1. This shortcut is supported for all the arithmetic operators.
Note that the variable you’re are reassigning must be the leftmost value in the expression. This means that x = 2 - x cannot be converted to an assignment operation.
Conclusion
We took a look at arithmetic operators that are common to all numeric Python data types, and the order in which they are evaluated in an expression. We also looked at how to simplify variable reassignment using assignment operations. Next time we’ll be taking closer look at the bool data type and Relational Operations.
