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Lists

Today we go over Lists in python and some built in functions and how they apply to them.

Instantiating A List

my_list = [1, 2, 3]
my_list2 = [2.3, 4.5, 6.2]
my_list3 = ["Chris", "Stayte", "Pyton"]
my_list4 = [1, 2.2, "Python"]
As you can see a list can contain any other data type as well as mutiple data types.


Accesing List Variables

my_list = [1, 2, 3]
print(my_list[0])
# prints 1
print(my_list[3])
# prints an error: out of index
print(my_list[0:3])
# prints [1, 2, 3]
# You can use '3' here becasue it tells 
# python where to stop and doesn't include it.
Keep in mind that the beginning index of all lists start at 0.


List Functions


Append

Add an item to the end of the list. Equivalent to a[len(a):] = [x].
my_list = [5, 10, 15, 20, 25, 30]

my_list.append(35)

# [5, 10, 15, 20, 25, 30, 35]


Clear

Remove all items from the list. Equivalent to del a[:].
my_list = [5, 10, 15, 20, 25, 30]

my_list.clear()

# []


Copy

Return a shallow copy of the list. Equivalent to a[:].
my_list = [5, 10, 15, 20, 25, 30]

my_list_2 = my_list.copy()
my_list_2.append(35)

# my_list = [5, 10, 15, 20, 25, 30]
# my_list_2 = [5, 10, 15, 20, 25, 30, 35]
Lists are passed by reference. If you want an actual copy of the list use this function.


Insert

Insert an item at a given position. The first argument is the index of the element before which to insert, so a.insert(0, x) inserts at the front of the list, and a.insert(len(a), x) is equivalent to a.append(x).
my_list = [5, 10, 15, 25, 30]

my_list.insert(3, 20)

# [5, 10, 15, 20, 25, 30]


Remove

Remove the first item from the list whose value is x. It is an error if there is no such item.
my_list = [5, 10, 15, 20, 25, 30]

my_list.remove(10)

# [5, 15, 20, 25, 30]


Pop

Remove the item at the given position in the list, and return it. If no index is specified, a.pop() removes and returns the last item in the list. (The square brackets around the i in the method signature denote that the parameter is optional, not that you should type square brackets at that position. You will see this notation frequently in the Python Library Reference.)
my_list = [5, 10, 15, 20, 25, 30]

number = my_list.pop(3)
# number = 20
# [5, 10, 15, 25, 30]


Reverse

Reverse the elements of the list in place.
my_list = [5, 10, 15, 20, 25, 30]

my_list.reverse()

# [30, 25, 20, 15, 10, 5]


Getting the number of items in a list

my_list = [5, 10, 15, 20, 25, 30]

print(len(my_list))

# Prints 6