C3 · Built-in Functions

Spec reference: Section C - Programming Paradigms
Key idea: Use arithmetic, string and general built-in functions to process data.

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▶ Variables and Data Types in Python

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What are built-in functions?

Built-in functions are pre-written functions provided by a programming language that perform common operations. You call them by name without needing to write the underlying code yourself.

They fall into three categories: arithmetic, string handling, and general.

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Arithmetic functions

Function	What it does	Example	Result
ROUND(x, n)	Round x to n decimal places	ROUND(3.7654, 2)	3.77
INT(x) / int(x)	Truncate to integer (remove decimal)	INT(7.9)	7
ABS(x)	Absolute value (remove negative sign)	ABS(-5)	5
SQRT(x)	Square root	SQRT(16)	4.0
MAX(a, b, ...)	Largest of the values given	MAX(3, 9, 1)	9
MIN(a, b, ...)	Smallest of the values given	MIN(3, 9, 1)	1

import math

print(round(3.7654, 2))    # 3.77
print(int(7.9))            # 7
print(abs(-15))            # 15
print(math.sqrt(25))       # 5.0
print(max(4, 9, 2))        # 9

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String handling functions

Strings are sequences of characters. String functions let you inspect, extract, and modify text.

Function	What it does	Example	Result
LEN(s)	Number of characters	LEN("Hello")	5
UPPER(s)	Convert to uppercase	UPPER("hello")	"HELLO"
LOWER(s)	Convert to lowercase	LOWER("HELLO")	"hello"
SUBSTRING(s, start, len)	Extract part of a string	SUBSTRING("Hello", 1, 3)	"Hel"
LEFT(s, n)	First n characters	LEFT("Hello", 3)	"Hel"
RIGHT(s, n)	Last n characters	RIGHT("Hello", 3)	"llo"
CONTAINS(s, t)	Does s contain t?	CONTAINS("Hello", "ell")	True

name = "Hello, World!"

print(len(name))             # 13
print(name.upper())          # HELLO, WORLD!
print(name.lower())          # hello, world!
print(name[0:5])             # Hello   (substring)
print("World" in name)       # True    (contains)
print(name.replace("World", "Python"))  # Hello, Python!

String indexing

Strings are zero-indexed in most languages:

H  e  l  l  o
0  1  2  3  4

So "Hello"[0] = 'H' and "Hello"[4] = 'o'.

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General functions

Function	What it does	Example	Result
STR(x)	Convert to string	STR(42)	"42"
INT(x)	Convert to integer	INT("42")	42
FLOAT(x)	Convert to float	FLOAT("3.14")	3.14
INPUT(prompt)	Get text input from user	INPUT("Enter name: ")	user's text
RANDOM(a, b)	Random integer between a and b	RANDOM(1, 6)	1 to 6

import random

user_age = int(input("Enter your age: "))  # input() + INT conversion
dice = random.randint(1, 6)
print("You rolled:", dice)

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Worked example: Name formatter

def format_name(first, last):
    # Capitalise first letter of each, combine
    first = first.strip().capitalize()
    last = last.strip().capitalize()
    full = first + " " + last
    initials = first[0] + last[0]
    return full, initials

name, init = format_name("alice", "smith")
print(name)     # Alice Smith
print(init)     # AS

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Test Yourself

Question 1 of 5

What does LEN("Computing") return?