User Input Handling

The input() function captures user-provided data, displaying an optional prompt. To enhance clarity, separate prompts from input areas using spaces.

user_input = input("What's for dinner tonight? ")
print(user_input)

For multi-line prompts, store the text in a variable first:

prompt_text = "Share your identity to view personalized info. "
prompt_text += "\nWhat's your full name? "
user_name = input(prompt_text)

Convert string inputs to numerical values using int():

age_str = input("How old are you? ")  # input() returns a string
user_age = int(age_str)
print(user_age > 18)

Determine even/odd numbers with the modulus operator (%), which returns division remainders:

num_str = input("Enter a number: ")
num = int(num_str)

if num % 2 == 0:
    print(f"{num} is even.")
else:
    print(f"{num} is odd.")

While Loop Fundamentals

While loops execute repeatedly untill a condition becomes false, unlike for loops that iterate over collections.

Basic Counting Loop

count = 1
while count < 5:
    print(count)
    count += 1

Termination via Condition Test

Exit when user enters a specific value:

topping_prompt = "Add a pizza topping (or 'none' to finish): "
user_choice = ""
while user_choice != "none":
    user_choice = input(topping_prompt)
    if user_choice != "none":
        print(f"Adding {user_choice} to your pizza.")

Flag-Controlled Loop

Use a boolean flag to manage loop state:

topping_prompt = "Add a pizza topping (or 'none' to finish): "
is_active = True
while is_active:
    choice = input(topping_prompt)
    if choice == "none":
        is_active = False
    else:
        print(f"Adding {choice} to your pizza.")

Break Statement for Early Exit

Immediately exit loops with break:

topping_prompt = "Add a pizza topping (or 'quit' to finish): "
while True:
    selection = input(topping_prompt)
    if selection == "quit":
        break
    print(f"Adding {selection} to your pizza.")

Continue Statement for Skipping Iterations

Skip remaining code in an iteration with continue:

i = 0
while i < 10:
    i += 1
    if i % 2 == 0:
        continue
    print(i)  # Prints odd numbers 1-9

Avoiding Infinite Loops

Ensure loop conditions eventual become false. For accidental infinite loops, use IDE termination shortcuts (e.g., Ctrl+C).

x = 0
while x < 3:  # Properly bounded to prevent infinity
    print(x)
    x += 1

List and Dictionary Processing

Transferring List Elements

Move items betweeen lists using pop():

order_list = ["egg sandwich", "veggie sandwich", "orleans sandwich"]
completed_orders = []

while order_list:
    current_order = order_list.pop()
    print(f"Preparing {current_order}")
    completed_orders.append(current_order)

print("Completed orders:", completed_orders)

Removing Specific Values

Eliminate all instances of a value from a list:

order_list = ["tuna sandwich", "veggie sandwich", "tuna sandwich", "ham sandwich"]
print("Tuna sandwiches sold out!")

while "tuna sandwich" in order_list:
    order_list.remove("tuna sandwich")

print("Updated orders:", order_list)

Populating Dictionaries with User Input

Collect survey responses into a dictionary:

survey_results = {}
is_polling = True

while is_polling:
    participant = input("Your name: ")
    destination = input("Dream vacation spot: ")
    survey_results[participant] = destination
    
    another = input("Add another participant? (yes/no): ")
    if another.lower() == "no":
        is_polling = False

print("\n--- Survey Results ---")
for name, place in survey_results.items():
    print(f"{name}'s dream spot: {place}")