Containers¶
Lists¶
Create an empty list¶
1 2 3 | new_list = list()
# or
new_list = []
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Create a list with items¶
1 | my_pets = ['euclid', 'leta']
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Add onto a list¶
1 | my_pets.append('socrates')
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Index into a list¶
1 2 3 | first_pet = my_pets[0]
second_pet = my_pets[1]
third_pet = my_pets[2]
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Slice a list into a new list¶
1 2 3 4 5 6 7 | # 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:]
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Test if a value is inside a list¶
1 2 3 4 5 6 | ## 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!")
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Sets¶
Create a set or convert a list to a set¶
1 2 3 4 5 6 7 8 9 10 | 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'])
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Add an item to a set¶
1 2 3 4 | my_new_set = set()
# instead of append, like a list, you use 'add'
my_new_set.add("Potatoes")
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Using sets to enforce uniqueness¶
1 2 3 4 5 6 | 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)
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