containers.rst

Containers

Lists

Create an empty list

new_list = list()
# or
new_list = []

Create a list with items

my_pets = ['euclid', 'leta']

Add onto a list

my_pets.append('socrates')

Index into a list

first_pet = my_pets[0]
second_pet = my_pets[1]
third_pet = my_pets[2]

Slice a list into a new list

# the syntax is
#   my_list[start:stop]
# this includes the start position but goes UP TO the stop
# you can leave either empty to go to the front or end

first_two_pets = my_pets[:2]
last_two_pets = my_pets[1:]

Test if a value is inside a list

## with any collection, you can test if an item is inside the collection
## it is with the "in" keyword

my_pets = ['euclid', 'leta']
if 'euclid' in my_pets:
    print("Euclid is a pet!")

Sets

Create a set or convert a list to a set

my_pet_list = ['euclid', 'leta']

# you can convert lists to sets using the set keyword
my_pet_set = set(my_pet_list)

# sets are like lists but you can't index into them or slice them
# they are used for fast membership testing

# you can create a new set by:
my_pet_set = set(['euclid', 'leta'])

Add an item to a set

my_new_set = set()

# instead of append, like a list, you use 'add'
my_new_set.add("Potatoes")

Using sets to enforce uniqueness

my_grocery_list = ['potatoes', 'cucumbers', 'potatoes']

# now if you want to make sure items only appear once, you can convert it to a set
# it will automatically do this for you, because items are only allowed to be in sets one time

my_grocery_set = set(my_grocery_list)