Solutions 02: Installation and Setup¶
Overview¶
Chapter 02 exercises are mostly verification and setup tasks rather than coding problems. This solution guide explains what correct output looks like, how to interpret it, and how to fix the most common problems.
Notes Before Checking Solutions¶
Most of these exercises have no single "correct" answer — the output depends on your operating system, Python version, and installation method. The goal is to confirm that Python is installed and working, not to match a specific string.
Warm-up Exercise Solutions¶
Exercise 1: Verify Your Python Installation¶
What correct output looks like:
or
Any version starting with 3.10 or higher is fine. If you see Python 2.7.x, that is Python 2 — you need to install Python 3 separately.
On macOS and Linux, the system Python is often Python 2. Use python3 instead of python:
On Windows, the Microsoft Store version of Python sets up python to point to Python 3. The python3 alias may or may not work depending on how you installed it.
If pip is missing:
This uses the pip bundled with Python directly. If that also fails, reinstall Python and make sure to check "Add pip" during installation.
Exercise 2: Explore the Python REPL¶
Expected outputs for each expression:
>>> 2 + 2
4
>>> "hello" + " world"
'hello world'
>>> len("Python")
6
>>> 10 / 3
3.3333333333333335
>>> 10 // 3
3
>>> 2 ** 8
256
Key observations:
- / always returns a float, even when the result is a whole number (10 / 2 gives 5.0).
- // is floor division — it rounds down to the nearest integer.
- ** is the exponentiation operator (not ^, which is bitwise XOR in Python).
- String concatenation with + works, but the strings must both be strings — "hello" + 5 raises a TypeError.
Exercise 3: Create Your First Python File¶
The expected output is exactly:
If you see nothing, the file may not have been saved. If you see an error, check:
1. The file is named hello.py (not hello.py.txt)
2. You are in the correct directory when you run python hello.py
3. The print call has parentheses — print("Hello, Python!") not print "Hello, Python!"
Practice Exercise Solutions¶
Exercise 4: Run a Script with User Input¶
How it works:
- input() pauses the program and waits for the user to type something and press Enter.
- Whatever the user types is returned as a string and stored in name.
- The f-string f"Hello, {name}!" inserts the value of name into the string at runtime.
Common mistake: Forgetting that input() always returns a string. If you need a number, you must convert it: age = int(input("Age: ")).
Exercise 5: Understand the Python Interpreter¶
import sys
print(f"Python version: {sys.version}")
print(f"Python executable: {sys.executable}")
print(f"Platform: {sys.platform}")
Example output on macOS:
Python version: 3.11.4 (main, Jul 5 2023, 13:45:01) [Clang 14.0.3]
Python executable: /usr/local/bin/python3
Platform: darwin
Example output on Windows:
Python version: 3.11.4 (tags/v3.11.4:d2340ef, Jun 7 2023, 05:45:37) [MSC v.1934 64 bit (AMD64)]
Python executable: C:\Users\Alice\AppData\Local\Programs\Python\Python311\python.exe
Platform: win32
sys.executable tells you exactly which Python binary is running. This is useful when you have multiple Python versions installed and want to confirm which one is active.
Exercise 6: REPL Calculations¶
The % operator returns the remainder after division. 100 % 7 = 2 because 7 * 14 = 98 and 100 - 98 = 2.
Exercise 7: Editor Run Button¶
There is no code to verify here. The key thing to confirm:
- The output panel shows Hello, Python!
- No error messages appear
If VS Code shows "Python extension not installed," install the Microsoft Python extension from the Extensions panel. It enables the run button, syntax highlighting, and IntelliSense.
Challenge Exercise Solutions¶
Challenge 1: Multi-Step Calculator¶
num1 = float(input("Enter first number: "))
num2 = float(input("Enter second number: "))
operation = input("Enter operation (+, -, *, /): ")
if operation == "+":
result = num1 + num2
elif operation == "-":
result = num1 - num2
elif operation == "*":
result = num1 * num2
elif operation == "/":
if num2 == 0:
print("Error: Cannot divide by zero.")
else:
result = num1 / num2
print(f"{num1} / {num2} = {result}")
else:
print(f"Unknown operation: {operation}")
result = None
if operation in ("+", "-", "*") or (operation == "/" and num2 != 0):
print(f"{num1} {operation} {num2} = {result}")
Why float() instead of int()? Using float() lets the calculator handle decimal numbers like 3.5. If you used int(), entering 3.5 would raise a ValueError.
Why check for division by zero? Dividing by zero raises a ZeroDivisionError. It is better to check for it explicitly and print a helpful message than to let the program crash.
A cleaner version separates the logic into a function:
def calculate(a, b, op):
if op == "+":
return a + b
elif op == "-":
return a - b
elif op == "*":
return a * b
elif op == "/":
if b == 0:
return "Error: Cannot divide by zero."
return a / b
else:
return f"Unknown operation: {op}"
a = float(input("Enter first number: "))
op = input("Enter operation (+, -, *, /): ")
b = float(input("Enter second number: "))
print(f"{a} {op} {b} = {calculate(a, b, op)}")
Challenge 2: Explore pip and Install a Package¶
This shows all installed packages. Common ones you will see even on a fresh install: pip, setuptools, wheel.
After installing, pip list should include requests and its dependencies (certifi, charset-normalizer, idna, urllib3).
import requests
response = requests.get("https://httpbin.org/get")
print(f"Status code: {response.status_code}")
A status code of 200 means the request succeeded. If you get a ConnectionError, check your internet connection.
Note: You will learn more about virtual environments in Chapter 15. For now, installing packages globally is fine for learning.
Challenge 3: Project Folder Structure¶
There is no code to verify. The goal is to build a habit of organizing your work. A clean folder structure makes it easier to find files and avoids confusion when you have dozens of scripts.
Suggested structure:
python-learning/
chapter-02/
hello.py
greet.py
check_python.py
calculator.py
chapter-03/
chapter-04/
Challenge 4: Virtual Environments (Preview)¶
python3 -m venv .venv
source .venv/bin/activate # macOS/Linux
.venv\Scripts\activate.bat # Windows CMD
.venv\Scripts\Activate.ps1 # Windows PowerShell
After activation, your prompt changes to show (.venv). Any packages you install now go into .venv/lib/ instead of the global Python installation.
This returns you to the global Python environment.
Why this matters: Virtual environments let each project have its own set of packages at specific versions. Without them, installing a package for one project can break another. Chapter 15 covers this in detail.
Common Mistakes¶
Using python when you need python3. On macOS and Linux, python often points to Python 2. Always check with python --version first.
Running scripts from the wrong directory. If you run python hello.py from a different folder, Python cannot find the file. Use cd to navigate to the correct folder first, or provide the full path.
Forgetting to save the file. Most editors show an unsaved indicator (a dot or asterisk in the tab). Always save before running.
Mixing tabs and spaces. Python requires consistent indentation. Configure your editor to insert 4 spaces when you press Tab.
What to Review Next¶
- Review the matching handbook chapter if any exercise felt difficult.
- Revisit the matching exercise set and try solving it again without looking at the solution.
- Continue with the next handbook chapter: Chapter 03 - Running Python