Manipulating_sequences

Question 1

mutable sequences can be modified how?

Answer 1

Replace elements
Delete elements
* often appended (to the end) .append()
* can also specify where in the sequence to .insert

Question 2

Replacing Single Elements

Answer 2

Replace an element at index 1 by assigning a new element to that index
l = [10, 20, 30]
l[1] = ‘hello’
l –> [10, ‘hello’, 30]

Question 3

Replacing an entire Slice

Answer 3

Just assign a new collection to the slice

my_list = [1, 2, 3, 4, 5]
my_list [0:3] = ['a', 'b']
my_list [0:3] = ('a', 'b')
my_list [0:3] = 'ab'
my_list --> ['a', 'b', 4, 5]

Python uses the elements of the sequence in RHS when assigning to a slice (but not when assigning using a single index)

Question 4

Deleting Elements

Answer 4

You can delete an element by index
~~~
my_list = [1, 2, 3, 4, 5]
del my_list[1]
my_list à [1, 3, 4, 5]
~~~

Question 5

Deleting Elements by slice

Answer 5

Can delete an entire slice

my_list = [1, 2, 3, 4, 5]
del my_list[1:3]
my_list à [1, 4, 5]

Question 6

Appending Elements

Answer 6

We can append one element

my_list = [1, 2, 3]
my_list.append(4)
my_list à [1, 2, 3, 4]

Question 7

To append multiple elements:

Answer 7

We extend the sequence

my_list = [1, 2, 3]
my_list.extend(['a', 'b', 'c'])
my_list.extend(('a', 'b', 'c'))
my_list.extend('abc')
my_list --> [1, 2, 3, 'a', 'b', 'c']

Question 8

Inserting an Element

Answer 8

Instead of appending, we can insert at some index
- use sparingly – this is much slower than appending or extending

my_list = [2, 3, 4, 5]
my_list.insert(0, 100)
my_list --> [100, 2, 3, 4, 5]

my_list = [2, 3, 4, 5]
my_list.insert(2, 100)
my_list --> [2, 3, 100, 4, 5]

Element is inserted so its position is the index - remaining elements are shifted right