Learn Python 3

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Reverse the elements in the list.

## Syntax

```py
list.reverse()
```

The `.reverse()` method does not take in any arguments.

## Example 1

```python
counting = [1, 2, 3, 4, 5]

counting.reverse()

print(counting)
# Output: [5, 4, 3, 2, 1]
```

## Example 2

To reverse a list called `hand`:

```codebyte/python
hand = ['Rock ✊', 'Paper 🖐', 'Scissors ✌️']

print('Original order: ', hand)

hand.reverse()

print('Updated order: ', hand)
```


.append()

The Python list method `.append()` adds an item to the end of a list.

## Syntax

```py
list.append(item)
```

The `.append()` will place the object passed in as a new element at the very end of the list. Printing the list afterwards will visually show the appended value.

This method is not to be confused with returning an entirely new list with the passed object.

## Example

To add `'🥚'` to the end of the `grocery` list:

```py
grocery = ['🍉', '🍪', '🥬', '🥕']

grocery.append('🥚')

print(grocery)
# Output: ['🍉', '🍪', '🥬', '🥕', '🥚']
```

## Codebyte Example

To add `'tulips'` to the end of the `orders` list:

```codebyte/python
orders = ['daisies', 'periwinkle']

orders.append('tulips')

print(orders)
```


Python

.clear()

The Python `.clear()` method removes all items from a list.

## Syntax

```py
list.clear()
```

The `.clear()` method has no parameters.

## Example

To remove all items from the `grocery` list:

```python
grocery = ['🍉', '🍪', '🥬', '🥕']

grocery.clear()

print(grocery)
# Output: []
```

## Codebyte Example

To remove all items from the `orders` list:

```codebyte/python
orders = ['daisies', 'periwinkle']

orders.clear()

print(orders)
```


.copy()

Returns a shallow copy of a list.

## Syntax

```py
list2 = list1.copy()
```

The `.copy()` method has no parameters.

## Example

A Python list can be copied using the `=` assignment operator:

```py
list1 = [1, 2, 3, 4]
list2 = list1

print(list1) # Ouptut: [1, 2, 3, 4]
print(list2) # Ouptut: [1, 2, 3, 4]
```

However, if you modify `list2`, `list1` is also modified. This is because `list2` is actually pointing to the `list1` object.

If you want the original list unchanged when the new list is modified, you can use the `.copy()` method.

Copying the `orders` list using `.copy()` method:

```codebyte/python
orders = ['daisies', 'periwinkle']

new_orders = orders.copy()

print(new_orders)
# Output: ['daisies', 'periwinkle']
```

Now if you change `new_orders`, `orders` stays the same.

## Shallow Copy

If you are copying nested lists, shallow copy means if you modify any of the new nested list elements, changes are reflected in both the new and old lists as they point to the same reference. Whereas in deep copy, if you modify any of the new nested list elements, only the new list changes.


Searches a list for a particular item and returns the number of matching entries found.

.count()

Searches a list for a particular item and returns the number of matching entries found.

## Syntax

```py
list.count(value, start, end)
```

The `.count()` method has three parameters:

- `value`: The string to search for. (Required)
- `start`: The index to start the search. Default is index 0.
- `end`: The position to end the search. Default is end of the string.

## Example 1

To count the number of `'pen'` within the `backpack` list:

```codebyte/python
backpack = ['pencil', 'pen', 'notebook', 'textbook', 'pen', 'highlighter', 'pen']

numPen = backpack.count('pen')

print(numPen)
# Output: 3
```

## Example 2

To count the number of `'pen'` within the `backpack` list from index 0 to index 5:

```codebyte/python
backpack = ['pencil', 'pen', 'notebook', 'textbook', 'pen', 'highlighter', 'pen']

numPen = backpack.count('pen', 0, 5)

print(numPen)
# Output: 2
```


.extend()

Adds list elements to end of the list.

## Syntax

```py
list.append(iterable)
```

This will place passed in iterable (list, tuple, or string) as new elements at the very end of the list.

`.append()` does not return any value.

## Examples

To add `grocery_new` to the end of the `grocery` list:

```codebyte/python
grocery = ['blueberries', 'eggs', 'artichoke']
grocery_new = ['milk', 'cookies']

grocery.extend(grocery_new)

print(grocery)
# Output: ['blueberries', 'eggs', 'artichoke', 'milk', 'cookies']
```

It works for any other type of iterables:

```codebyte/python
to_do_list = ['respond to email', 'check github']
targets = (4, 1, 6, 20)

to_do_list.extend(targets)

print(to_do_list)
# Output: ['respond to email', 'check github', 4, 1, 6, 20]
```


Finds the first occurence of a particular value within the list.

.index()

Finds the first occurence of a particular value within the list.

## Syntax

```py
list.index(value, start, end)
```

The `.index()` list method has three parameters:

- `value`: The string to search for. (Required)
- `start`: The index to start the search. Default is index 0.
- `end`: The position to end the search. Default is end of the string.

## Example 1

To find the index the first `'pen'` within the `backpack` list:

```codebyte/python
backpack = ['pencil', 'pen', 'notebook', 'textbook', 'pen', 'highlighter', 'pen']

firstPen = backpack.index('pen')

print(firstPen)
# Output: 1
```

## Example 2

To find the index the first `'pen'` within the `backpack` list within index 3 to index 6:

```codebyte/python
backpack = ['pencil', 'pen', 'notebook', 'textbook', 'pen', 'highlighter', 'pen']

firstPen = backpack.count('pen', 3, 6)

print(firstPen)
# Output: 4
```


Adds an item at a specified index in the list.

.insert()

Adds an item at a specified index in the list.

## Syntax

```py
list.insert(index, item)
```

The `.insert()` method takes in two parameters:

- The index that you want to insert into.
- The item that you want to insert at the specified index.

## Example

To add an item at index 2 of `store_line` list:

```codebyte/python
store_line = ['Karla', 'Maxium', 'Martim', 'Isabella']

store_line.insert(2, 'Vikor')

print(store_line)
# Output: ['Karla', 'Maxium', 'Vikor', 'Martim', 'Isabella']
```


Removes an item from a list while also returning it.

.pop()

Removes an item from a list while also returning it.

## Syntax

```py
list.pop(index)
```

It accepts one optional input which is the index of the element to remove. If no index is provided, then the last element in the list will be removed and returned.

## Example

To pop the element `'Discrete Math'` from the `courses` list:

```codebyte/python
courses = ['Into to Programming', 'Data Structures & Algorithms', 'Databases', 'Discrete Math', 'Computer Architecture']

courses.pop(3)

print(courses)
# Output: ['Into to Programming', 'Data Structures & Algorithms', 'Databases', 'Computer Architecture']
```

## Example 2

If no index is provided:

```codebyte/python
courses = ['Into to Programming', 'Data Structures & Algorithms', 'Databases', 'Discrete Math', 'Computer Architecture']

courses.pop()

print(courses)
# Output: ['Into to Programming', 'Data Structures & Algorithms', 'Databases', 'Discrete Math']
```


Remove an item from a list by passing in the value of the item to be removed as an argument.

.remove()

Remove an item from a list by passing in the value of the item to be removed as an argument.

## Syntax

```py
list.remove(item)
```

In the case where two or more elements in the list have the same value, the first occurrence of the element is removed.

## Example

To remove the first occurance of `'eggs'`:

```codebyte/python
grocery_list = ['blueberries', 'mochi', 'eggs', 'chocolate']

grocery_list.remove('eggs')

print(grocery_list)
# Output: ['blueberries', 'mochi', 'chocolate']
```


.reverse()

Sort the contents of the list it is called on.

.sort()

Sort the contents of the list it is called on.

## Syntax

```py
list.sort()
```

Numerical lists will be sorted in ascending order, and lists of strings will be sorted into alphabetical order. It modifies the original list, and has no return value.

## Example

To sort a list called `exampleList`:

```codebyte/python
exampleList = [4, 2, 1, 3]

exampleList.sort()

print(exampleList)
# Output: [1, 2, 3, 4]
```


.reverse()

Syntax

Example 1

Example 2

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