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Section 1. Introduction to Function & Module

Functions: Like a Microwave Preset Button

1. Real-life analogy:
   • Preset buttons = Predefined functions
   • “Popcorn” button = def popcorn_mode()
   • “Beverage” button = def reheat_drink()
2. Python example:

def start_microwave(preset):
    if preset == "popcorn":
        print('heat for 180 seconds')
    elif preset == "beverage":
        print('heat for 45 seconds')

start_microwave("popcorn")

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Why do We Need Functions

Problem without functions:

# Making 3 sandwiches
print("1. Get bread")
print("2. Add filling")
print("3. Close sandwich")
print("------")
print("1. Get bread")
print("2. Add filling")
print("3. Close sandwich")
print("------")
print("1. Get bread")
print("2. Add filling")
print("3. Close sandwich")

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Creating Our First Function

Solution with functions:

def make_sandwich():
    print("1. Get bread")
    print("2. Add filling")
    print("3. Close sandwich")
    print("------")

make_sandwich()
make_sandwich()
make_sandwich()

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Making Functions Flexible

Adding parameters:

def make_sandwich(filling):
    print(f"Making {filling} sandwich:")
    print("1. Get bread")
    print("2. Add "+ str(filling))
    print("3. Close sandwich")
    print("------")

make_sandwich("ham")
make_sandwich("cheese")

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Modules: Like Game Sound Library

1. Real-life example:
   • Game sound module = import sound_effects
   • Ready-to-use sounds = jump_sound(), explosion_sound()
2. Simple Python example:
   ```python

   sound_module.py

   def play_jingle(): print(“🎵 Happy tune playing! 🎵”)

main.py

import sound_module sound_module.play_jingle()

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# Building Our Own Module
1. Create `kitchen.py`:  
```python
def microwave_beep():
    print("BEEP! BEEP! BEEP!")

def oven_timer():
    print("DING! Food is ready!")

1. Use it:

   import kitchen
   kitchen.microwave_beep()
   kitchen.oven_timer()
   

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Example: Cooking Module

Complete example:

# In cooking_module.py
def prepare_dish(dish_name):
    print("Preparing "+str(dish_name)+"...")
    print("1. Gather ingredients")
    print("2. Follow recipe steps")

# In main program
import cooking_module
cooking_module.prepare_dish("pasta")
cooking_module.prepare_dish("salad")

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Example: Game Sounds

# sound_effects.py
def laser_blast():
    print("PEW! PEW! ")

def power_up():
    print(" ENERGY RESTORED!")

# game.py
import sound_effects
sound_effects.laser_blast()
sound_effects.power_up()

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Key Takeaways

1. Functions are like preset shortcuts
2. Parameters make functions flexible
3. Modules help organize code
4. Import lets reuse code
5. Combine functions/modules for complex programs

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Section 2. Function Basic Syntax

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What is a Function?

Like a recipe:

1. Receive ingredients (parameters)
2. Follow steps (code block)
3. Give result (return value)

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Function Structure

def magic_oven(ingredient):  # Function header
    output=str(ingredient) +" cookie" #  Function body
    return(output)   

Three essential parts:

1. def statement with function name
2. Action-performing code block
3. return the result (optional)

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Demo 1: Greeting

def greet(name):
    print("Hello, "+str(name))


greet("Alice")  # Output: Hello, Alice!
greet("Bob")    # Output: Hello, Bob!

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Question: How can we write a function that only greets to Alice?

Question: How can we write a function that greets Bob in another way?

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Shape-Shifting Greetings (Multiple Parameters)

def flexible_greet(name, greeting):
    print(str(greeting)+' '+str(name)+'!')

flexible_greet("Charlie", "Good morning")  # 
flexible_greet("Diana", "Ni hao")          # 
flexible_greet("Eric", "Guten Tag")        # 

Parameters order matters!

(greeting, name) vs (name, greeting)

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Calculator Function (Return Value)

def circle_area(radius):
    area =  3.14 * radius ** 2
    return(area)

print(circle_area(5))  # 78.5
print("Pizza area:", circle_area(30))  # 

pizza_price = circle_area(30) * 0.02

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Common Mistakes

Case 1: Missing Colon

# Wrong
def bad_function()
    print("Oops")

# Right
def good_function():
    print("Yay!")

Case 2: Wrong Indentation

# Wrong
def messy_function():
print("No indent!")

# Right
def clean_function():
    print("Perfect!")

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Parameter-Free Functions

import datetime

def show_time():
    now = datetime.datetime.now()
    print("Current time: "+str(now.hour)+':'+str(now.minute))

show_time()  

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Multi-Parameter Function (BMI)

def calculate_bmi(weight, height):
    """Calculate Body Mass Index"""
    bmi=weight / (height ** 2)
    return(bmi)

print("BMI:", calculate_bmi(70, 1.75))  
print("BMI:", calculate_bmi(65, 1.68)) 

Health tip:
Normal BMI range: 18.5 - 24.9

Question: BMI and weight => height

Question: x1/2 vs. x(1/2)

Question: How can we check the correctness of “BMI and weight => height”?

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Function Superpowers

1. Reusable code blocks
2. Clear program structure
3. Easy error tracking
4. Team collaboration

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Section 3. Advanced Parameters & Return Values

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Positional vs Keyword Arguments

Pizza Ordering System Example

def make_pizza(size, toppings):
    print("Making "+str(size)+"cm pizza with:")
    for topping in toppings:
        print(topping)

# Positional arguments
make_pizza(30, ["mushrooms", "olives"])

# Keyword arguments
make_pizza(toppings=["cheese"], size=20)

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When to Use Keyword Arguments?

1. When passing many parameters
2. When parameters have default values
3. To improve code readability

Try this bad example:

# Confusing positional arguments
make_pizza(["pepperoni"], 25)

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Default Parameters

Shipping Cost Calculator

def calculate_shipping(weight, base_fee=5.0):
    price=weight * 1.2 + base_fee
    return(price)

print(calculate_shipping(3.5))       # Uses default base_fee
print(calculate_shipping(2.0, 4.0))  

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Multiple Return Values

Box Dimension Calculator

def box_calculator(length, width, height):
    volume = length * width * height
    surface = 2 * (length*width + length*height + width*height)
    return(volume, surface)  # Returns a tuple!

dimensions = box_calculator(5, 3, 2)
print("Volume: "+str(dimensions[0])+", Surface: "+str(dimensions[1]))

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Unpacking Return Values

# Direct unpacking
vol, surf = box_calculator(2, 2, 2)
print("Perfect cube: "+str(vol)+" cubic units")

# Works with different variable names
v, s = box_calculator(1, 3, 5)

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Variable Scope Experiment

temperature = 25  # Global variable

def adjust_temp():
    temperature = 18  # Local variable
    print("Inside: "+str(temperature)+"°C")

adjust_temp()
print("Outside: "+str(temperature)+"°C")  # Still 25

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Global Keyword Demo

score = 0

def update_points():
    global score
    score = score+10
    print("New score: "+str(score))

update_points()  # Now modifies the global variable

print(score)

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Good Function Names

# Good examples
def calculate_tax(income):
def get_user_profile(id):
def convert_to_fahrenheit(celsius):

# Bad examples
def tax(inc):          # Too vague
def user(id):          # Verb missing
def temp_conv(c):      # Unclear abbreviation

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Function Name Checklist

1. Use underscore separation
2. Be specific but concise
3. Keep under 3 words when possible

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Summary

Key concepts covered:

1. Argument types (positional/keyword)
2. Default parameter values
3. Returning multiple values
4. Variable scope
5. Naming best practices

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Section 4. Python Modules System

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Today’s Learning Goals

• Understanding different import methods
• Working with Python standard libraries
• Creating and using custom modules
• Namespace concept

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Basic Module Import Methods

Full Module Import

import math

print(math.sqrt(25))  # 5.0
print(math.pi)        # 3.141592653589793

![Down Arrow] Key points:

• Access elements with dot notation
• Avoids naming conflicts

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Specific Function Import

from random import randint

lottery = [randint(1, 50) for _ in range(6)]
print("Winning numbers:", lottery)

Example output:

Winning numbers: [14, 37, 5, 23, 42, 19]

![Warning] Be careful with name collisions!

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Math Library in Action

import math

a = 3
b = 4
c = math.sqrt(a**2 + b**2)
print(f"The hypotenuse is: {c}")

Output:

The hypotenuse is: 5.00

Question: change f-string (f”The hypotenuse is: {c}”) into “+” format.

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Random Library Fun

from random import choice

participants = ["Alice", "Bob", "Charlie", "Diana"]
winner = choice(participants)
print(f"Congratulations {winner}!")

Possible output:

Congratulations Charlie!

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Time Library Demo

import time

print("Starting countdown:")
for i in range(5, 0, -1):
    print(i)
    time.sleep(1)


print("Blast off! ")

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Creating Your First Module

1. Create mymodule.py:

   def greet(name):
    return f"Hello {name}, from my module!"
   

2. In main program: ```python import mymodule

print(mymodule.greet(“Sarah”))

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### Understanding Namespaces
```python
import math
import mymath  # Hypothetical custom math module

print(math.sqrt(16))  # 4.0
print(mymath.sqrt(16)) # Maybe different implementation

![Toolbox Analogy] Each module is like a separate toolbox

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Exploring Third-Party Libraries

# requests example
import requests

response = requests.get("https://www.bioinfo-lab.com/")
print(f"Status code: {response.status_code}")
print(f"Response time: {response.elapsed.total_seconds()}s")

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Module Search Path

import sys

print("Python looks in these locations:")
for path in sys.path:
    print("- "+str(path))

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Import Best Practices

1. Keep imports at top of file
2. Use aliases for long names:

import numpy as np
import pandas as pd

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Section 5. Practical Python Examples for Beginners

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Roadmap

1. Auto-generated Password Program
2. Simple Calculator
3. Temperature Conversion System

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Example 1: Password Generator (1/2)

Problem: Create random secure passwords

import random

def generate_password(length=8):
    chars = "abcdefghijkmnpqrstuvwxyz23456789"
    this_password =''
    i=1
    while(i<=length):
        this_password=this_password+random.choice(chars)
        i=i+1
    return(this_password)

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Example 1: Password Generator (2/2)

Usage:

print(generate_password())   # Example: 'a3x7bk9m'
print(generate_password(12)) # Example: 'wxn58k2q9yr7'

Question: how can we add random uppercase and lowercase characters?

Hint: random.random(), lower(), upper()

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Example 2: Simple Calculator (1/2)

Core logic:

def calculator(a, b, operator="+"):
    if operator == "+":
        return a + b
    elif operator == "-":
        return a - b

Question: how can we add “*” and “/”?

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Example 2: Simple Calculator (2/2)

Using our calculator:

print(calculator(5, 3))           # 8 (uses default +)
print(calculator(5, 3, "-"))      # 2
print(calculator(2.5, 4, "+"))    # 6.5

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Example 3: Temperature Converter (1/2)

Conversion formulas:

Celsius to Fahrenheit: (C × 9/5) + 32

def c_to_f(c):
    return (c * 9/5) + 32

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Example 3: Temperature Converter (2/2)

Test conversions:

print(c_to_f(0))
print(c_to_f(100))

Question: write the function “f_to_c”

Question: How can we check the correctness of “f_to_c”

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