Composite Data Types

Composite Data Types

What is in this lesson?

Composite data types Enumerations Dictionaries and Sets in Python 11th January 2026 Tram Tran 2

Primitive Data Types (recap)

Primitive data types are the basic, built-in data types in programming languages. They represent single values and are immutable. ▶ int: integer numbers ▶ float: real numbers ▶ bool: carry one of two values True or False ▶ char: one single character Primitive data types are essential for creating more complex data types called composite data types. 11th January 2026 Tram Tran 3

Composite data types

▶ Composite data types are complex, user-defined structures built from primitives data types. ▶ They are either included in the programming language or created by programmers. ▶ array ▶ tuple ▶ dict ▶ set ▶ Classes and Objects ▶ Abstract data types representing complex entities in a program 11th January 2026 Tram Tran 4

Composite Data Types: An Example Let’s take student data as an example. 11th January 2026 Tram Tran 5

Composite Data Types: An Example Let’s take student data as an example. 11th January 2026 Tram Tran 5

C Structures (struct)

▶ A struct in C is a programmer-created data type that combines different types of variables in a structure variable. ▶ The variables are calledstruct members. struct Date { int day; char month[10]; int year; }; struct Date d;

d.day = 5;
d.year = 2026;
int y = d.year;

11th January 2026 Tram Tran 6

Python Classes [1, Ch. 10] A class specifies the attributes and methods for a particular type. 1 class Date: 2 def __ ini t_ _ (self, day: int, month: str, year: int):

3 self . day = day
4 self . month = month
5 self . year = year

▶ The self parameter is required in every method of a class. It references the specific object that the method is supposed to operate on. ▶ The __init__ method is known as an initialiser method since it initialises the object’s data attributes. 11th January 2026 Tram Tran 7

Using Composite Data Types

▶ In Python, class is considered as a blueprint of the custom data type that we define. ▶ To use it as a variable for storing custom data, we need to create an instance of the class.

1 d = Date (5 , " January " , 2026)

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Datetime Composite Data Type in Python Python provides a built-indatetime module for handling dates and times. 1 from da tet im e import date 3 # Create a date object for January 05, 2026

4 m e e t i n g _ d a t e = date ( year =2026 , month =1 , day =5)

6 print (m e e t i n g _ d a t e) 7 # Output: 2026 -01 -05 11th January 2026 Tram Tran 9

Nested Composite Data Types

A composite data type can have fields/ members/ attributes that are also composite data types. 1 class Date: 2 def __ ini t_ _ (self, day: int, month: str, year: int):

3 self . day = day
4 self . month = month
5 self . year = year

7 class Booking: 8 def __ ini t_ _ (self, room: str, date: Date, time: str):

9 self . room = room
10 self . date = date
11 self . time = time

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Enumerations

C Enumerations (enum)

▶ Enumeration is a composite data type, holds constant values. ▶ Enumeration assigns meaningful names to a set of integers. enum Month {

JANUARY = 1, FEBRUARY, MARCH, APRIL, MAY, JUNE,

JULY, AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER

}; 11th January 2026 Tram Tran 11

struct Date { int day; enum Month month; int year;

}; int main() {

enum Month m = JANUARY;

printf("Month number: %d\n", m); return 0; } 11th January 2026 Tram Tran 12

enum Month {

JANUARY = 1, FEBRUARY, MARCH, APRIL, MAY, JUNE,

JULY, AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER

}; ▶ Enumerations are by default numbered incrementally in ascending order; ▶ but you can break this by explicitly defining the number directly. ▶ enum values start at 0 by default. ▶ In C, anenum is internally represented as anint. 11th January 2026 Tram Tran 13

Why use constants and enumerations?

▶ To give meaning to numbers, improve readability ▶ Prevent errors ▶ Easier to maintain ▶ Logical grouping of related values 11th January 2026 Tram Tran 14

Dictionaries and Sets in Python

Dictionaries [1, Ch. 9]

Concept A dictionary is an object that stores a collection of data. ▶ Each element in a dictionary has a pair of: key and value. ▶ A key is used to locate a specific value. ▶ You can create a dictionary by enclosing the elements inside a set of curly braces ({}).

1 p h o n e b o o k = {

2 ’ Chris ’: ’ 555 -1111 ’, 3 ’ Katie ’: ’ 555 -2222 ’, 4 ’ Joanne ’: ’ 555 -3333 ’ 5 } 11th January 2026 Tram Tran 15

Retrieving, Adding, and Removing Dictionary Elements [1, Ch. 9] ▶ Retrieve a value: 1 < dictionary_name >[ < key >] ▶ Add a new key-value pair or assign a value to an existing key:

1 < dictionary_name >[ < key >] = < value >

▶ Remove an existing key-value pair: 1 del < dictionary_name >[ < key >] 11th January 2026 Tram Tran 16

The in and not in Operators [1, Ch. 9] ▶ Accessing a nonexistent key in a dictionary raises aKeyError. ▶ Use thein operator to check if a key exists before accessing it. ▶ Use not in to check if a key does not exist. 1 if ’ Chris ’ in p h o n e b o o k: 2 print (p h o n e b o o k [ ’ Chris ’ ]) 4 if ’ Tom ’ not in p h o n e b o o k: 5 print (’ Tom is not found. ’) 11th January 2026 Tram Tran 17

Iterate over a Dictionary [1, Ch. 9] You can use thefor loop to iterate over all the keys in a dictionary. 1 for < key > in < dictionary >: 2 < statement > 3 < statement > ▶ This loop iterates once for each element in the dictionary. ▶ Each time the loop iterates, the variable<key> is assigned a key. 11th January 2026 Tram Tran 18

Sets [1, Ch. 9]

Concept A set is an object that stores a collection of unique values in the same way as mathematical sets. ▶ All the elements in a set must be unique. ▶ Sets are unordered. ▶ The elements that are stored in a set can be of different data types. 1 # Create an empty set

2 myset = set ()

3 # Create a set with some e lem en ts

4 myset = set ([ ’a ’ , ’b ’ , ’c ’ ])

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Adding and Removing Elements [1, Ch. 9] ▶ Add a new element: 1 < Set >. add (< value >) ▶ Remove an existing element: 1 < Set >. remove (< value >) ▶ Discard an element: 1 < Set >. discard (< value >) The only difference betweenremove and discard is that when the specified item is not found in the set, theremove method raises a KeyError, but thediscard method does not. 11th January 2026 Tram Tran 20

Iterate over a Set [1, Ch. 9] You can use thefor loop to iterate over all the elements in a set. 1 for < element > in < Set >: 2 < statement > 3 < statement > Similarly, you can use thein and not in operators to check if an element exists in a set. 11th January 2026 Tram Tran 21

Set Operations [1, Ch. 9]

Given two setsset1 and set2, in Python:
▶ set1∪set2
1 set1 . union ( set2 )
2 set1 | set2
▶ set1∩set2
1 set1 . i n t e r s e c t i o n ( set2 )
2 set1 & set2
▶ set1\ set2
1 set1 . d i f f e r e n c e ( set2 )
2 set1 - set2
▶ set1⊆set2
1 set1 . i ss ubs et ( set2 )
▶ set1⊇set2
1 set1 . i s s u p e r s e t ( set2 )

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Recap

In this lecture, we’ve learned: ▶ What are composite data types, and what are some composite data types in C and Python? ▶ Nested composite data types ▶ Enumerations in C ▶ Dictionaries and Sets in Python 11th January 2026 Tram Tran 23

References

Gaddis, TonyStarting out with Python. Pearson Education Limited. Sixth Edition, 2024. 11th January 2026 Tram Tran 24

Any Question?