Week 03: Python basics and control flow
There are three main ways to execute Python code, each with different use cases:
uv run python script.py - Execute a Python file in the course environmentuv run python -c "print('Hello World')" - Run a single commanduv run python - Start the managed interactive Python shellPython development has evolved with modern tools that make coding faster and more reliable:
uv.lockuv run python script.py - Run scripts in the project environmentuv sync --locked to reproduce the environment and uv run python -m pytest to run tests=) to put data into variablessnake_case for variable names (PEP 8 Style Guide)# Good variable names (descriptive and clear)
student_name = "Grace Hopper"
birth_year = 1906
is_computer_pioneer = True
course_grade = 95.7
print(f"Student: {student_name}")
print(f"Born: {birth_year}")
print(f"Pioneer: {is_computer_pioneer}")
print(f"Grade: {course_grade}")
# Poor variable names (avoid these)
n = "Grace Hopper" # What is 'n'?
x = 1906 # What does 'x' represent?snake_case (words separated by underscores)
user_name, calculate_total, is_validSCREAMING_SNAKE_CASE (all caps)
MAX_ATTEMPTS = 3, PI = 3.14159PascalCase (capitalize each word)
StudentRecord, BankAccount, WeatherDatalowercase or snake_case
math, user_authentication# Multiple assignment
name, age, grade = "Alice", 20, "A"
print(f"{name} is {age} years old with grade {grade}")
# Tuple unpacking from a function return
def get_student_info():
return "Bob", 21, 3.8
student_name, student_age, gpa = get_student_info()
print(f"{student_name}: age {student_age}, GPA {gpa}")
# Chained assignment
x = y = z = 0
# Augmented assignment operators
score = 85
score += 10 # Same as: score = score + 10
score *= 2 # Same as: score = score * 2str (string): Text data, enclosed in quotes (' or ")int (integer): Whole numbers, positive or negativefloat (floating-point): Numbers with decimal pointsbool (boolean): Truth values (True or False)type() function: Use this to check what type a variable is# Python automatically determines types
student_name = "Ada Lovelace" # str
student_id = 12345 # int
gpa = 3.95 # float
is_honors_student = True # bool
graduation_year = None # NoneType
# Check types
print(type(student_name)) # <class 'str'>
print(type(gpa)) # <class 'float'>
print(type(is_honors_student)) # <class 'bool'>\n (newline), \t (tab).upper(), .lower(), .strip(), .replace()# Different ways to create strings
name = 'Alan Turing'
name = "Alan Turing" # Equivalent
quote = """Computing machinery and intelligence
was published in 1950 by Alan Turing."""
# Escape sequences
message = "Hello\nWorld\t!" # Hello(newline)World(tab)!
file_path = "C:\\Users\\Documents\\file.txt" # Windows path
# String methods
name = " alan turing "
print(name.strip().title()) # "Alan Turing"
print(name.upper()) # " ALAN TURING "
print(name.replace("alan", "Alan")) # " Alan turing "1.5e3 means 1.5 × 10³ = 1500+, -, *, /, // (floor division), % (modulo), ** (exponent)int(), float(), str()# Integer examples
students_enrolled = 150
temperature_celsius = -5
big_number = 123456789012345678901234567890 # No limits!
print(f"Students: {students_enrolled}")
print(f"Temperature: {temperature_celsius}C")
# Float examples
pi = 3.14159
temperature_fahrenheit = 23.0
scientific = 1.5e6 # 1,500,000
print(f"Pi: {pi}, scientific: {scientific}")
# Arithmetic operations
result = 17 / 3 # 5.666666666666667 (regular division)
result = 17 // 3 # 5 (floor division)
result = 17 % 3 # 2 (remainder)
result = 2 ** 10 # 1024 (exponentiation)
# Type conversions
age_str = "21"
age_int = int(age_str) # Convert string to integer
pi_str = str(3.14159) # Convert float to stringinput() function: Gets text from user via keyboardint() or float() for numeric input# Simple string input
name = input("What is your name? ")
print(f"Hello, {name}!")
# Numeric input with conversion
age_str = input("What is your age? ")
age = int(age_str) # Convert to integer
# One-liner for numeric input
grade = float(input("Enter your grade (0-100): "))
# Multiple inputs
print("Tell me about yourself:")
name = input("Name: ")
age = int(input("Age: "))
favorite_color = input("Favorite color: ")
print(f"Hi {name}! You're {age} and love {favorite_color}.")f"Hello {name}!" - preferred method.format() method: "Hello {}!".format(name) - older but still common"Hello %s!" % name - legacy, avoid in new codename = "Katherine Johnson"
salary = 75000.50
accuracy = 0.99999
# f-string examples (Python 3.6+)
print(f"Employee: {name}")
print(f"Salary: ${salary:,.2f}") # $75,000.50
print(f"Accuracy: {accuracy:.2%}") # 99.99%
print(f"Name width: {name:>20}") # Right-aligned
# .format() method examples
print("Hello {}! You earned ${:,.2f}".format(name, salary))
print("Accuracy: {:.1%}".format(accuracy))
# Complex f-string expressions
items = ["apple", "banana", "cherry"]
print(f"We have {len(items)} fruits: {', '.join(items)}")
# Multi-line f-strings
report = f"""
Employee Report:
Name: {name}
Salary: ${salary:,.2f}
Performance: {accuracy:.1%}
"""type() and print() to inspect values# Common debugging techniques
name = input("Enter name: ")
print(f"Debug: name = '{name}', type = {type(name)}")
# Check if conversion worked
age_str = input("Enter age: ")
try:
age = int(age_str)
print(f"Successfully converted '{age_str}' to {age}")
except ValueError:
print(f"Couldn't convert '{age_str}' to a number")Mad Libs Generator Preview:
def generate_mad_lib(adjective, noun, verb):
"""
Generates a short story using the provided words.
This function is testable and reusable!
"""
# Your task: Create a story using f-string formatting
# Must include all three parameters in the returned string
# Example structure: f"Once upon a time, a {adjective} {noun}..."
pass
# How it will be used (conceptual - you'll implement the function)
# word1 = input("Give me an adjective: ")
# word2 = input("Give me a noun: ")
# word3 = input("Give me a past-tense verb: ")
# result = generate_mad_lib(word1, word2, word3)
# print(result) # Should print your creative story!Suggested reading before our next class:
Why this matters: - The supplied workflow repeats the Week 03 tests after a push - The Actions log provides a second source of evidence in addition to local tests - Lab 03 asks you to use the workflow, not create or edit it
True or False==, !=, <, >, <=, >=# Simple condition
temperature = 75
if temperature > 70:
print("It's warm outside!")
print("Perfect for a walk.")
# Multiple conditions
age = 20
has_id = True
if age >= 21 and has_id:
print("Welcome to the club!")
elif age >= 18:
print("You can vote, but can't enter the club.")
else:
print("Too young for either.")== (equal), != (not equal), <, >, <=, >=and, or, notis, is not (check if same object)in, not in (check if item in collection)not → comparisons → and → or# Comparison examples
score = 85
grade = "B"
is_passing = score >= 60 # True
is_excellent = score >= 90 # False
is_b_grade = grade == "B" # True
# Logical operators
has_homework = True
studied_hard = False
can_pass = has_homework and studied_hard # False
should_study = not studied_hard # True
might_pass = has_homework or studied_hard # True
# Membership testing
fruits = ["apple", "banana", "cherry"]
has_apple = "apple" in fruits # True
has_orange = "orange" not in fruits # True
# Complex conditions
username_is_valid = True
password_is_valid = True
is_admin = False
if username_is_valid and password_is_valid and not is_admin:
print("Regular user login successful")for loops: When you know what you want to iterate overwhile loops: When you want to repeat until a condition changesbreak (exit loop), continue (skip to next iteration)# For loop with range()
print("Countdown:")
for i in range(5, 0, -1):
print(f"{i}...")
print("Blast off!")
# For loop with collections
students = ["Alice", "Bob", "Charlie"]
for student in students:
print(f"Hello, {student}!")
# While loop for user input
total = 0
while total < 100:
number = int(input("Enter a number (goal: reach 100): "))
total += number
print(f"Current total: {total}")
print("Goal reached!")
# Loop with break and continue
for i in range(10):
if i == 3:
continue # Skip 3
if i == 7:
break # Stop at 7
print(i) # Prints: 0, 1, 2, 4, 5, 6range() function: a loop companionrange(stop): Numbers from 0 to stop-1range(start, stop): Numbers from start to stop-1range(start, stop, step): Numbers from start to stop-1, incrementing by steplist(range(5)) to see all values# Basic range patterns
print(list(range(5))) # [0, 1, 2, 3, 4]
print(list(range(1, 6))) # [1, 2, 3, 4, 5]
print(list(range(0, 10, 2))) # [0, 2, 4, 6, 8]
print(list(range(10, 0, -1))) # [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
# Practical examples
# Print multiplication table
number = 7
for i in range(1, 11):
print(f"{number} x {i} = {number * i}")
# Process items with indices
fruits = ["apple", "banana", "cherry"]
for i in range(len(fruits)):
print(f"Item {i}: {fruits[i]}")
# Better way: enumerate()
for i, fruit in enumerate(fruits):
print(f"Item {i}: {fruit}")Number Guessing Game Preview:
import random
def guessing_game():
"""Play the guessing game described in the Lab 03 contract."""
secret = random.randint(1, 100)
attempts = 0
while True:
guess = int(input("Enter your guess: "))
# TODO: count the attempt
# TODO: print "Too low!", "Too high!", or the success message
# TODO: exit the loop after the correct guessrandom, math, datetimeuv manages Python, dependencies, environments, and lockfilesuv sync creates an isolated project environmentrequests (web), pandas (data), flask (web apps)# Standard library examples
import random
import math
import datetime
# Random numbers for games, simulations
lucky_number = random.randint(1, 10)
coin_flip = random.choice(["heads", "tails"])
# Mathematical functions
area = math.pi * (radius ** 2)
square_root = math.sqrt(16)
# Date and time operations
today = datetime.date.today()
formatted = today.strftime("%B %d, %Y")
# Coming later: third-party packages
# In the terminal for your own project: uv add requests
# import requests
# response = requests.get("https://api.github.com/users/bgreenwell")pytesttest_, functions start with test_assert statements to check results# In your lab03.py file
def add_numbers(a, b):
"""Add two numbers and return the result."""
return a + b
# In test_lab03.py file
def test_add_numbers():
"""Test that add_numbers works correctly."""
result = add_numbers(2, 3)
assert result == 5
result = add_numbers(-1, 1)
assert result == 0
result = add_numbers(0, 0)
assert result == 0# The supplied Week 03 workflow follows this pattern
name: run-pytest
on: [push] # Run when code is pushed
jobs:
build:
runs-on: ubuntu-latest # Fresh Linux machine
steps:
- uses: actions/checkout@v6 # Get your code
- uses: astral-sh/setup-uv@c771a70e6277c0a99b617c7a806ffedaca235ff9
with:
enable-cache: true
- name: Install dependencies
run: uv sync --locked
- name: Test with pytest
run: uv run python -m pytest # Run all testsWhat you’ll build:
generate_mad_lib(adjective, noun, verb)guessing_game()week03/lab03.py, push, and confirm the Week 03 badge is greenKey learning outcomes: - Practice strings, conditionals, loops, input, and functions - Use deterministic tests for random numbers and keyboard input - Read failures locally before pushing
Use the current lab instructions as the source of truth:
week03/lab03.mduv run --directory week03 python -m pytest tests/ -vweek03/lab03.pyRemember: A green Week 03 badge represents the complete 10-point lab.
IS 4010: App Dev with AI