Adding and Removing Items

Section 27.5 Adding and Removing Items

Sometimes, we do not know all of the items in a list in advance - we want to build up a list as the program is running. To do this, we can start with a blank list using [] as our list. And then we can use append to add things to the end of the list.

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Checkpoint 27.5.1.

This program adds two strings to the list words. Add code to add the word “Carrot” to the list after “Banana” but before “Date”

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It is also possible to add items to locations other than the end of the list by using the insert function. To use it, we provide an index of where to insert the new value with the value we want to insert. Try running this sample with codelens:

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Checkpoint 27.5.2.

What happens if you use an index that does not exist to insert? Change the last insert in the sample above to insert at location 200 instead of 2. What happens?

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The item just does not get added
Try it!
There is an error and the program stops
Try it!
The item is added to the end of the list
Correct
The list is extended to be long enough that there is an item index 200
Try it!

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To remove items from a list, there are two main options:

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pop() removes an item from the end of a list. (It “pops” the item off.)
pop(index) removes an item from the specified index.
remove(value) removes the first copy of the specified value from the list.

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This sample shows all three methods:

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Checkpoint 27.5.3.

We want the list called alphabet to contain the letters “A”, “B”, “C”, “D” in that order. Use a combination of append, insert, remove, and pop to make it have the right values.

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(Do not use letters[index] to change the existing items.)

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Checkpoint 27.5.4.

The following program should make the discounts list contain the values of all the items from price_list after they have been discounted by 50%. To do so, we need to loop through the original prices, calculate the discounted price, then append it to the discount list.

Put the blocks in the right order. There are some blocks you will not use.

price_list = [21.99, 25.99, 19.99, 10.99, 15.99]
discounts = []
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for price in price_list:
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 new_price = price * .50
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 discounts.append(new_price)
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print(discounts)
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for price in discounts:  #distractor
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 price.append(price_list)  #distractor

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