Lecture 02 — Python: The Language of AI

~2–3 hours (core recap lecture)

🐍 Why Python?

Python is the language of thinking for AI and algorithms.

It is used in:

• 🤖 Artificial Intelligence
• 📊 Data Science
• 🧠 Research & prototyping
• 🧩 Coding interviews (LeetCode, Google, Meta)

If you know Python well, you can think clearly.

🧠 Mental Model (IMPORTANT)

Before syntax, remember this:

Python executes line by line, top to bottom.
Variables point to objects.
Everything is an object.

This mental model helps you avoid 80% of bugs.

1️⃣ Variables & Data Types

📦 Variables

x = 10
name = "AI"
pi = 3.14
is_active = True

Python is dynamically typed:

x = 10
x = "now a string"

🔢 Core Data Types

❓ Quiz

2️⃣ Control Flow (if / else)

x = 5

if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")

🧠 Interview Tip

Indentation is logic in Python.

❓ Quiz

3️⃣ Loops (for / while)

🔁 for-loop (most common)

for i in range(5):
    print(i)

🔄 while-loop

count = 0
while count < 3:
    print(count)
    count += 1

🧠 Interview Tip

Use for unless you must use while.

❓ Quiz

4️⃣ Lists (Most Important for LeetCode)

nums = [1, 2, 3, 4]

Common operations

nums.append(5)
nums.pop()
nums[0]
nums[-1]
len(nums)

Looping over list

for n in nums:
    print(n)

With index

for i, n in enumerate(nums):
    print(i, n)

❓ Quiz

5️⃣ Strings (Text = Sequence)

s = "machine"

Strings behave like lists:

s[0]        # 'm'
s[-1]       # 'e'
s[1:4]      # 'ach'

Useful methods

s.lower()
s.upper()
s.split()

❓ Quiz

6️⃣ Dictionaries (Key–Value Thinking)

student = {
    "name": "Kao",
    "age": 25,
    "major": "AI"
}

Access

student["name"]
student.get("age")

Loop

for key, value in student.items():
    print(key, value)

🧠 Interview Tip

Dictionaries give O(1) average lookup.

❓ Quiz

7️⃣ Sets (Uniqueness)

nums = [1, 2, 2, 3]
unique = set(nums)

Use cases

• Remove duplicates
• Fast membership check

if 3 in unique:
    print("Found")

❓ Quiz

8️⃣ Functions (Reusable Thinking)

def add(a, b):
    return a + b

Default arguments

def greet(name="AI"):
    print("Hello", name)

❓ Quiz

9️⃣ Common Built-ins (LeetCode Gold)

len()
sum()
min()
max()
sorted()
range()

Example:

nums = [3, 1, 2]
sorted(nums)

🔟 Time Complexity Awareness (VERY IMPORTANT)

Python coding interviews are algorithm interviews, not syntax tests.

🧠 Python for AI Mindset

Python is:

• 🧩 How we express logic
• 🧠 How we describe algorithms
• 🤖 How we talk to machines

Clean Python = Clear Thinking