Python- Day 22- Using a While Loop with Lists and Dictionaries

Handling Multiple User Inputs:

• While loops can collect and manage multiple inputs by storing them in lists or dictionaries.
• Unlike for loops, while loops can modify lists during execution, making them useful for dynamically managing data like user inputs.

Moving Items Between Lists:

You can transfer items from one list to another using a while loop.

In this example, we start with a list of unverified users and an empty list for confirmed users. As we verify each user, we move them from the unverified list to the confirmed list using a while loop.

# Start with users that need to be verified,
# and an empty list to hold confirmed users.
unconfirmed_users = ['alice', 'brian', 'candace']
confirmed_users = []

# Verify each user until there are no more unconfirmed users.
# Move each verified user into the list of confirmed users.
while unconfirmed_users:
    current_user = unconfirmed_users.pop()  # Remove the last unverified user
    print(f"Verifying user: {current_user.title()}")
    confirmed_users.append(current_user)  # Add the user to the confirmed list

# Display all confirmed users.
print("\nThe following users have been confirmed:")
for confirmed_user in confirmed_users:
    print(confirmed_user.title())

>>

Verifying user: Candace
Verifying user: Brian
Verifying user: Alice

The following users have been confirmed:
Candace
Brian
Alice

• The while loop runs as long as unconfirmed_users is not empty.
• The pop() method removes the last user from unconfirmed_users and assigns it to current_user.
• Each verified user is added to confirmed_users using append().
• Once all users are confirmed, the loop ends, and the program prints the confirmed users.

Removing Specific Values from a List:

To remove all instances of a specific value (e.g., removing all ‘cat’ entries from a list), use a while loop.

Suppose we have a list with multiple instances of a specific value, like ‘cat’, and we want to remove all occurrences. The while loop repeatedly removes 'cat' until none remain.

# List of pets with multiple 'cat' entries
pets = ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
print("Original list of pets:", pets)

# Remove all instances of 'cat' from the list
while 'cat' in pets:
    pets.remove('cat')

print("Updated list of pets:", pets)

>>

Original list of pets: ['dog', 'cat', 'dog', 'goldfish', 'cat', 'rabbit', 'cat']
Updated list of pets: ['dog', 'dog', 'goldfish', 'rabbit']

• The while loop checks if 'cat' is still present in the pets list.
• If ‘cat’ is found, it removes the first occurrence of it using remove().
• The loop repeats until all instances of ‘cat’ are removed.

Filling a Dictionary with User Input:

A while loop can gather input from users and store it in a dictionary, associating a user’s response with their name.

In this example, we create a polling program where users are asked a question, and their answers are stored in a dictionary. Each user’s name is the key, and their response is the value.

# Empty dictionary to store responses
responses = {}

# Set a flag to indicate that polling is active.
polling_active = True

while polling_active:
    # Prompt for the person's name and response
    name = input("\nWhat is your name? ")
    response = input("Which mountain would you like to climb someday? ")

    # Store the response in the dictionary
    responses[name] = response

    # Ask if another user wants to respond
    repeat = input("Would you like to let another person respond? (yes/no) ")
    if repeat.lower() == 'no':
        polling_active = False

# Polling is complete, display the results
print("\n--- Poll Results ---")
for name, response in responses.items():
    print(f"{name} would like to climb {response}.")

>>


What is your name? Nidhi
Which mountain would you like to climb someday? Mount Everest
Would you like to let another person respond? (yes/no) yes

What is your name? Nid
Which mountain would you like to climb someday? Eastern Himalaya        
Would you like to let another person respond? (yes/no) no

--- Poll Results ---
Nidhi would like to climb Mount Everest.
Nid would like to climb Eastern Himalaya.

• The while loop keeps running as long as polling_active is True.
• The program prompts the user for their name and the mountain they would like to climb.
• The response is stored in the responses dictionary, where the key is the user’s name, and the value is their response.
• The user is then asked if they want to allow another person to respond. If they type ‘no’, the loop ends by setting polling_active = False.
• After polling ends, the program prints all responses.

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