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Week 3: More Data Types, File I/O, Functions & Scope

Why Learn This?

This week introduces essential tools that make your programs more powerful and flexible:

  • Work with more complex data types like lists and dictionaries.
  • Read and write to files for real-world data interaction.
  • Create reusable blocks of logic with functions.
  • Understand scope — a critical concept for debugging and larger programs.

These skills are essential for data science, backend development, and automation tasks.

Concepts & Notes

More Data Types

List

fruits = ["apple", "banana", "cherry"]
print(fruits[0])       # apple
fruits.append("date")
print(len(fruits))     # 4

Tuple (immutable list)

coords = (10, 20)
print(coords[1])       # 20

Set (no duplicates)

unique_nums = {1, 2, 3, 1}
print(unique_nums)     # {1, 2, 3}

Dictionary (key-value pairs)

person = {"name": "Coder", "age": 30}
print(person["name"])  # Coder

File I/O

Write to a File

with open("output.txt", "w") as f:
    f.write("Hello file!")

Read from a File

with open("output.txt", "r") as f:
    content = f.read()
    print(content)

Functions & Scope

Define a Function

def greet(name):
    return "Hi, " + name

print(greet("Pythonista"))  # Hi, Pythonista

Default Parameters

def add(x, y=5):
    return x + y

print(add(3))  # 8

Args and Kwargs

def show_args(*args, **kwargs):
    print("Args:", args)
    print("Kwargs:", kwargs)

show_args(1, 2, a="apple", b="banana")

Scope

x = "global"

def my_func():
    x = "local"
    print(x)  # local

my_func()
print(x)      # global

Quiz – Week 3

  1. Which data structure is immutable: list, set, tuple, or dict?

  2. What is the output of set([1, 2, 2, 3])?

  3. How do you write to a file in Python?

  4. What does *args do in a function definition?

  5. What will this function return?

    def foo(x=1, y=2): return x + y
print(foo())

  6. What is the scope of a variable declared inside a function?

Coding Challenges – Week 3

Challenge 1: Create a Shopping List

Instructions: Create an empty list, add three items using .append(), and print the list.

Learning Objective: Use Python’s list methods to manage a dynamic collection.

# TODO: Create an empty list, add three items using `.append()`, and print the list.

Challenge 2: Count Word Frequencies

Instructions: Given a string, count how many times each word appears using a dictionary.

Learning Objective: Learn how to use dictionaries to store frequency counts.

# TODO: Given a string, count how many times each word appears using a dictionary.

Challenge 3: Save User Input to File

Instructions: Ask the user for their name and write it to a text file.

Learning Objective: Practice writing to files using Python's with open().

# TODO: Ask the user for their name and write it to a text file.

Challenge 4: Read & Print File Contents

Instructions: Open a file and print its contents line by line.

Learning Objective: Reinforce file reading using a context manager.

# TODO: Open a file and print its contents line by line.

Challenge 5: Function to Double a Number

Instructions: Write a function double(x) that returns x * 2.

Learning Objective: Practice defining and calling functions.

# TODO: Write a function `double(x)` that returns `x * 2`.

Challenge 6: Print Arguments and Keyword Arguments

Instructions: Write a function that uses *args and **kwargs and prints them out.

Learning Objective: Understand how to handle variable argument lists in functions.

# TODO: Write a function that uses `*args` and `**kwargs` and prints them out.

Week 3 Summary

  • You learned about four powerful data types: lists, tuples, sets, and dictionaries.
  • You wrote to and read from files — an essential real-world programming skill.
  • You defined and called functions to encapsulate reusable logic.
  • You learned about scope and how variables behave inside vs. outside functions.
  • You saw how to handle any number of inputs with *args and **kwargs.

These skills allow you to start building real applications, handle structured data, and write modular code.

For Next Week

Reading

Assignments

First:

Then, complete the following exercises -- you can, of course, do them all:

  • 02_more_datatypes
    • 02_02_product_largest.py
    • 02_06_tupled_words.py
    • 02_10_pairing_tuples.py (challenging)
    • 02_12_add_or_not.py
    • 02_14_char_count_dict.py
    • 02_16_inspiring_quotes.py
    • 02_19_comprehension_syntax.py
  • 03_file-input-output
    • 03_01_long_words.py
    • 03_03_writing.py
  • 04_functions-and-scopes
    • 04_02_mind_the_order.py
    • 04_03_write_letter.py
    • 04_05_docstring_me.py
    • 04_07_determine_divisible.py
    • 04_08_calculate_stats.py