Python for AI 102

Acknowledgement: This post is based mainly on Dr. Quang-Vinh Dinh’s presentation and slides and partly on on TA, STA, and peers’ responses from the course, AIO2025, offered by AI VIETNAM.

Relevance: The audience of this lecture were those who have learned Python for AI 101, had some coding experience, and known a bit of AI knowledge. Absolute beginners are encouraged to read the material and repeatedly practice coding without AI assistance to strengthen their coding and code-reading skills. Note that only necessary Python knowledge is introduced here.

When you get a result that is not what you expect, do not ask for help immediately. Instead, run the code by hand to figure out where your logic breaks, modify the program, and run it again. Repeat this process and your skills will be through the roof at breakneck speed.
-Dr. Quang-Vinh Dinh

In today’s post, we’ll look at common errors and loops in Python.

Common Errors

If you’ve tried some Python exercises, you probably have encountered some of the errors we’ll mention shortly.

NameError

NameError occurs when you try to use a variable or function that hasn’t been defined.

a = 7 
Print(a)

c = a + b
print(c)

def a_function(x): 
    a_variable = 4
    return x * a_variable

print(a_variable)

SyntaxError

SyntaxError occurs when a program violates some grammatical rule of the language.

s = 'Hello World"

print(s)

ZeroDivisorError

ZeroDivisorError occurs when a program tries to perform division by zero, which is mathematically incorrect.

a = 7
b = 0

c = a / b
print(c)

TypeError

TypeError occurs when there is an incompatible data type operation in a program.

a = 5
s = 'AI'

c = a + s
print(c)

IndexError

IndexError occurs when a program attempts to access an element of a collection (a list or string) through an index outside the valid range for that sequence.

a_list = [1, "love", "aivietnam"]

print(a_list[3])

IndentationError

IndentationError signifies the incorrect or inconsistent use of whitespace (spaces or tabs) in a program.

a = 7 
    b = 8

print(b)

ValueError

ValueError occurs when a program attempts to perform an operation on a value that is of correct data type but makes the operation mathematically invalid.

import math

number = -4
print(math.sqrt(number))

ModuleNotFoundError

ModuleNotFoundError occues when a program cannot locate a module that it attempts to import.

import mymodule

print("iloveaivietnam")

RecursionError

RecursionError occurs when a recusive functions calls itself infinitely many times, exceeding Python’s default recusion limit.

def a_function(n):
    return a_function(n)

a_function(7)

print "hello world"

a = 5
Print(a)

import math

number = 220.3
print(math.floor(number)
print(math.pi)

numbers = list(range(10))

for i in numbers:
    if numbers[i] == 5:
        numbers.remove(i)

a = 5
c = a + b
print(c)

s = 'hello world'
print(s[100])

number = 15

if number < 10
    print('A smaller number')
else: 
    print('A larger number')

import torch

print(torch.cuda.is_available())

def a_function(x):
    a_var = 4
    result = x * a_var

    return result

print(a_var)

Suppose we want to draw a million stars. It’d take forever to complete this task unless we, I guess, desire to be professional star drawers. There must be a way to avoid such an endlessly repetitive action. Exactly, it’s a loop, which repeats some action within itself. In Python, there are two types of loops including for and while loops.

For Loop

# code before for

for element in iterable:
    # code inside for

# code after for

flowchart LR
    title[For Loop Flowchart]
    title --> A[start]
    style title fill:#FFF, stroke:#FFF, font-style:italic, font-size:30
    linkStyle 0 stroke:#FFF, stroke-width:0, marker-end:none;

    A --> B{stop condition} 
    B --->|True| C[inside for] --> D[step] --> B
    B ---->|False| E[end for]

    style B fill:#ffdab9
    style C fill:#c6f777
    style D fill:#c6f777

A for loop is used when the number of times we want to iterate over a sequence, also known as an iterable.

• An iterable can be a string, list, dictionary, tuple, and range().
• An element’s name can be almost anything but is usually i or _.
• The body must be indented.

For now, we’ll focus on the range(start, stop, step) function.

• start is $0$ and step is $1$ by default. Passing arguments to these parameters is optional.
• The stop value is required.
• The loop runs through a range from start, increases by step, and goes up to but not including stop.

Let’s look at some examples.

# repeat 3 times
for i in range(3):
    print(i)

# repeat 3 times
value = 5
for i in range(3):
    print(value + i)

# repeat 5 times
total = 0
for i in range(5):
    total = total + i
    print(total)

for i in range(5):
    total = 0
    total = total + i
    
print(total)

product = 0
for i in range(5):
    product = product * i

print(product)

product = 1
for i in range(5):
    product = product * i

print(product)

While Loops

# code before while

while condition:
    # code inside while

# code after while

flowchart LR
    title[While Loop Flowchart]
    title --> A[start]
    style title fill:#FFF, stroke:#FFF, font-style:italic, font-size:30
    linkStyle 0 stroke:#FFF, stroke-width:0, marker-end:none;

    A --> B{while condition}
    B --->|True| C[inside while] --> B
    B --->|False| D[end while]

    style B fill:#ffdab9
    style C fill:#c6f777

• A while loop is used when we do not know the number of iterations.
• A while loop runs as long as conditions are fulfilled.

Always update the condition inside the loop. Or else, we may create/encounter an infinite loop which runs forever unless we force it to quit.

num= 1
a_list = [0, 1, 2]
while True == num in a_list:
    print("helloaivietnam")

    # remove the last time of a_list
    a_list.pop()

Keywords Used in Loops

break

Imagine playing Where’s Waldo? and we know exactly how many objects there are on the page. Our goal is simple: find Waldo and stop immediately. Also think about a number-guessing game. We’d have to keep guessing until we hit the correct number. The moment we do, the game ends.

In both cases, we need to use a loop to repeat tasks, but a strong command is needed to exit early when the goal is met. That’s where break comes in!

The break keyword is mainly used to terminate a loop regardless of whether a for loop finishes its iterations or a while loop is no longer satisfied. Simply put, when the program hits the break keyword, it breaks out of the loop.

for x in range(7):
    print(x)

    if x == 5:
        break

print("iloveaivietnam")

for x in range(7):
    if x == 5:
        break

    print(x)

print("iloveaivietnam")

import random

while True:
    roll = random.randint(1, 6)
    print(f"You rolled {roll}.")

    if roll == 6:
        print("You win!")
        break

continue

Imagine building a machine that scans a conveyor belt of strawberries. The goal is to pick up only the ripe ones and skip the unripe without stopping the belt. Here, a loop goes through every strawberry but magically ignores those unripe. The magic word for this scenario is continue.

The continue keyword is to skip the rest of the current round and jump straight to the next. This keyword is less common than break.

for x in range(7):
    print(x)

    if x == 5:
        continue

print("iloveaivietnam")

for x in range(7):
    if x == 5:
        continue

    print(x)

print("iloveaivietnam")

Examples and Exercises

FAQ

Here are some good questions asked during class. The answers to these questions came from either some admin, TA, STA, or members of AIO2025.