Data Types

int, float, str, bool

Numeric Data Types

Read Inferential Thinking

Read Ch 4 intro and Ch 4.1, which describes in detail how Python evaluates expressions involving numeric data types.

Before continuing, make sure you understand the following:

Every value has a type (data type), and the built-in type function returns the type of the result of any expression.
In Python, integers are called int values. Real numbers are called float values. These are flexible but have some computational limitations.
The type of an expression is the type of its final value.
When a float value is combined with an int value using some arithmetic operator, then the result is always a float value.

Summary of Numeric Operators

You have seen this table before.

Common Python operators for numeric data types
Operator	Symbol	Example Expression	Expression Value
Addition	`+`	`2 + 3`	5
Subtraction	`-`	`15 - 4`	`11`
Multiplication	`*`	`-2 * 9`	`-18`
Division	`/`	`15 / 2`	`7.5`
Integer division	Cuts off remainder	`//`	`15 // 2`
Remainder/Modulo	`%`	`19 % 3`	`1` (19 ÷ 3 = 6 Remainder 1)
Exponentiation	`**`	`3 ** 2`	`9`

Strings

Read Inferential Thinking

Read Ch 4.2 which describes the string data type.

Before continuing, make sure you understand the following:

A string is a text data type. It can use single quotes or double quotes.
The meaning of an expression depends both upon its structure and the types of values that are being combined.

Concatenation operation: The + operator works differently on string data types. Instead of adding numerically, it “adds textually,” which is more formally called concatenation:

2 + 3  # addition

'hello' + "donuts"

'hellodonuts'

Length function: There is one function not shown above that would be useful to you know, and that is len(s), which takes a string argument and returns its length.

s = "hello world"
len(s)

Boolean Data Type

The Boolean data type (bool) has exactly two values: True and False. Note that boolean values are not strings!

b = True
b

True

b = False
type(b)

bool

In our current view of Python as an advanced calculator, it may be unclear why such a special data type is needed. We will find soon that it is very useful to have a special data type to represent whether something is true or false.

Typecasting

We can also typecast, or convert values between data types. These typecasting functions take in one typed argument and return another typed argument, then return that value as a different type. The function name is generally the type. Note that data type conversion is only valid “when it makes sense.” We’ll talk about this more later.

x = 3       # what type is x?
str(x)      # returns a value of type string

'3'

s = "5"       # what type is x?
float(s)      # what type is returned?

5.0

External Reading

(mentioned in notes) Computational and Inferential Thinking, Ch 4 intro, Ch 4.1, Ch 4.2
(optional) Tomas Beuzen. Python Programming for Data Science Ch 1.2.