Update lists.md

episodes/lists.md

@@ -18,10 +18,10 @@ exercises: 10
 ::::::::::::::::::::::::::::::::::::::::::::::::::
 
 ## A list stores many values in a single structure.
-The most popular kind of data collection in Python is the list. Lists have two primary important characteristics:
+A list is one of the most commonly used data structures in Python. Lists have two important characteristics:
 
-1. They are mutable, i.e., they can be changed after they are created.
-2. They are heterogeneous, i.e., they can store values of many different types.
+1. They are `mutable`, i.e, they can be changed after they are created.
+2. They are `heterogeneous`, i.e, they can store values of many different types.
 
 To create a new list, you can just put some values in square brackets with commas in between. Let's create a short list of some library metadata standards.
 
@@ -76,7 +76,7 @@ List is now: ['bibframe', 'frbr', 'mets', 'mods']
 
 ### Character strings are immutable.
 
-Unlike lists, we cannot change the characters in a string using its index value. In other words strings are *immutable* (cannot be changed in-place after creation), while lists are *mutable*: they can be modified in place. Python considers the string to be a single value with parts, not a collection of values.
+Unlike lists, we cannot change the characters in a string using its index value. Strings and lists can both be indexed and sliced. However, strings are immutable (cannot change in place), while lists are mutable.
 
 ```python
 librarian = 'Langanathan' # misspelled SR Ranganathan's name
@@ -100,9 +100,16 @@ f'First item in sublist: {mixed_list[2][0]}'
 First item in sublist: 10
 ```
 
-## Appending items to a list lengthens it.
+## Using list methods to make adding/removing easier.
 
-Use `list_name.append` to add items to the end of a list. In Python, we would call `.append()` a *method* of the list object. You can use the syntax of `object.method()` to call methods.
+Lists are **objects**, which means they provide methods that allow us to perform common operations. A **method** is called using the syntax `object.method()`.
+
+Lists provide methods for modifying their contents. We call these methods using dot notation. There are many methods associated with a list, but we will cover only a few of them.
+
+
+### Appending items to a list.
+
+Use `list_name.append()` to add items to the end of a list. In Python, we would call `.append()` a *method* of the list object. 
 
 ```python
 print(f'list was:{metadata}')
@@ -115,22 +122,55 @@ list was: ['bibframe', 'frbr', 'mets', 'mods']
 list is now: ['bibframe', 'frbr', 'mets', 'mods', 'oai-pmh']
 ```
 
-## Use `del` to remove items from a list entirely.
+We can also call `list_name.insert(index, value)` to add an item at a given position in the list. The first argument specifies where to place the new item, and the second argument is the item to add.
+
+```python
+numbers = [1, 2, 3, 4, 6]
+print(f'numbers before: {numbers}')
+numbers.insert(4, 5)
+print(f'numbers after: {numbers}')
+```
+
+```output
+numbers before: [1, 2, 3, 4, 6]
+numbers after: [1, 2, 3, 4, 5, 6]
+```
+
+### Removing items from a list.
+
+Use `list_name.pop()` to remove and return the last item in a list. If we provide an index, `.pop()` removes and _returns_ the item at that position. It raises an IndexError if the list is empty or the index is out of range.
 
-`del list_name[index]` removes an item from a list and shortens the list. Unlike `.append()`, `del` is not a method, but a "statement" in Python. In the example below, `del` performs an "in-place" operation on a list of prime numbers. This means that the `primes` variable will be reassigned when you use the `del` statement, without needing to use an assignment operator (e.g., `primes = ...`) .
 
 ```python
-primes = [2, 3, 5, 7, 11]
-print(f'primes before: {primes}')
-del primes[4]
-print(f'primes after: {primes}')
+drinks = ['water', 'tea', 'coffee', 'milk']
+print(f'drinks before: {drinks}')
+drinks.pop()
+print(f'drinks after first pop: {drinks}')
+val = drinks.pop(0)
+print(f'drinks after second pop: {drinks}')
+print(val)
 ```
 
 ```output
-primes before: [2, 3, 5, 7, 11]
-primes after: [2, 3, 5, 7]
+drinks before: ['water', 'tea', 'coffee', 'milk']
+drinks after first pop: ['water', 'tea', 'coffee']
+drinks after second pop: ['tea', 'coffee']
+water
+```
+
+We can also call `list_name.remove(value)`, where value is the item you want to remove. This will remove the **first** occurrence of the item. If there are multiple, then `.remove()` will need to be called several times. 
+
+```python
+animals = ['dog', 'bird', 'shark', 'dog']
+print(f'animals before: {animals}')
+animals.remove('dog')
+print(f'animals after: {animals}')
 ```
 
+```output
+animals before: ['dog', 'bird', 'shark', 'dog']
+animals after: ['bird', 'shark', 'dog']
+```
 
 :::::::::::::::::::::::::::::::::::::::  challenge
 
@@ -223,8 +263,8 @@ print(f'second time: {values}')
 ```
 
 ```output
-first time [1, 3, 5]
-second time [3, 5]
+first time: [1, 3, 5]
+second time: [3, 5]
 ```
 
 :::::::::::::::::::::::::
@@ -239,12 +279,13 @@ second time [3, 5]
 Run the following code on your own and answer the following questions.
 
 ```python
-resources = ['books','DVDs','maps','databases']
+resources = ['books', 'DVDs', 'maps', 'databases']
 print(resources[-1])
 ```
 
 1. How does Python interpret a negative index value?
-2. If `resources` is a list, what does `del resources[-1]` do?
+2. If `resources` is a list, what does `resources.pop(-1)` do?
+3. What value does `resources.pop(-1)` return?
 
 :::::::::::::::  solution
 
@@ -256,7 +297,7 @@ databases
 
 1. A negative index begins at the final element.
 2. It removes the final element of the list.
-
+3. It will return the final element of the list.
 
 :::::::::::::::::::::::::
 
@@ -268,8 +309,7 @@ databases
 - A list stores many values in a single structure.
 - Use an item's index to fetch it from a list.
 - Lists' values can be replaced by assigning to them.
-- Appending items to a list lengthens it.
-- Use `del` to remove items from a list entirely.
+- Use list methods to help add and remove items
 - Lists may contain values of different types.
 - Character strings can be indexed like lists.
 - Character strings are immutable.