3. Data Types

See: https://www.w3schools.com/python/python_datatypes.asp

3.1. Data type categories

Type Category	Data Type
TextType	str
NumericTypes	int, float, complex
SequenceTypes	list, tuple, range
MappingType	dict
SetTypes	set, frozenset
BooleanType	bool
BinaryTypes	bytes, bytearray, memoryview
NoneType	NoneType

3.2. Data type examples

Example	Data Type	Type Category	Mutability	Ordered	Structure
text = “Hello, World!”	str	Text Type	Immutable	Ordered	in single ‘’ or double quotes “”
integer = 42	int	Numeric Type	Immutable	Unordered	whole numbers
floating_point = 3.14	float	Numeric Type	Immutable	Unordered	decimals
complex_number = 1 + 2j	complex	Numeric Type	Immutable	Unordered	real + imaginary numbers
my_list = [1, 2, 3, 4]	list	Sequence Type	Mutable	Ordered	square brackets []
my_tuple = (1, 2, 3, 4)	tuple	Sequence Type	Immutable	Ordered	parentheses ()
my_range = range(1, 10)	range	Sequence Type	Immutable	Ordered	range function
my_set = {1, 2, 3, 4}	set	Set Type	Mutable	Unordered	{} with unique items
my_frozenset = frozenset([1, 2, 3, 4])	frozenset	Set Type	Immutable	Unordered	frozenset() with unique items
my_dict = {“name”: “Anne”, “age”: 28}	dict	Mapping Type	Mutable	Ordered	{} with key-value pairs
is_valid = True	bool	Boolean Type	Immutable	Unordered	True or False
nothing = None	NoneType	None Type	Immutable	Unordered	None
my_bytes = b”Hello”	bytes	Binary Type	Immutable	Unordered	b”” or b’’
my_ba = bytearray([65, 66, 67])	bytearray	Binary Type	Mutable	Unordered	bytearray()

3.3. Strings

A string is a sequence of characters surrounded by either single quotation marks (' ') or double quotation marks (" ").

Using Quotes Within Strings: - If your text contains single quotes, you can use double quotes to enclose the string.
- Example: "It's a nice day."
- If your text contains double quotes, you can use single quotes to enclose the string. - Example: 'Jane said "Go now", then left.'`
Using Both Quotes Within Strings: - If your text contains both single and double quotes, you can use triple quotes to enclose the string.
- Example: '''My favourite quote from Jane's essay was "Go now". Short and sweet.'''
Escaping Quotes: - You can use the backslash (``) to escape quotes within a string, forcing them to be used literally.
- Example: ‘It's a nice day.’

Triple Quotes for Documentation and Multi-line Strings: - Triple quotes (either ''' or """) are used for documentation strings (docstrings) and multi-line strings.

Example of a docstring for a function:

def square_number(n):
    """
    This function returns the square of a given number.

    Parameters:
    n (int or float): The number to be squared.

    Returns:
    int or float: The square of the input number.
    """
    return n ** 2

Example of a multi-line string:

"""This is a multiline string.
It can span multiple lines.
You can include line breaks."""

3.4. Numbers

Numbers are written without quotes.
An integer is a whole number.
e.g. 2
A float is a decimal.
e.g. 3.5

3.5. Booleans

Booleans have the value True or False.

3.6. Types

The type() function can be used to get the data type for a variable.

# String
print(type('hello'))   # <class 'str'>

# Integer
print(type(1))         # <class 'int'>

# Float
print(type(1.64))      # <class 'float'>

# Boolean
print(type(True))      # <class 'bool'>

# None
print(type(None))      # <class 'NoneType'>

Questions

Predict the output from print(type('123')).
Predict the output from print(type(123)).
Predict the output from print(type('False')).

3.7. Type casting

See: https://www.w3schools.com/python/python_casting.asp

The conversion of one type to another is called type casting.

Data types can’t be mixed so type casting is needed to convert data to the same type so that they can be used together.

3.7.1. Converting numbers to strings

str() converts a number to a string with a number in it

j = str(3.01) # j will be "3.01"

An integer can be converted to a string using the str() function.

The premierships integer is converted to a string so it can be combined with the rest of the strings for printing.

team = 'Richmond'
premierships = 11
print(team + ' has won ' + str(premierships) + ' premierships.')

3.7.2. Converting numbers as strings to numbers

int() converts a string consisting of an integer to an integer number

c = int("3")      # c will be 3

float() converts a string consisting of a decimal to a decimal number

g = float("4.23") # g will be 4.23

Questions

Predict the output from print(int(2.5)).
Predict the output from print(int("3")).
Predict the output from print(float(1)).
Predict the output from print(float("4.23")).
Predict the output from print(str(3.01)).