Lists and Dictionaries

Lists

Create a list

people = []                                # empty list
animals = ['daisy','pat','wabbit','bunny']

Access elements

print(animals[0])                        # first item
print(animals[-1])                       # last item
print(animals[-2])                       # penultimate item
print(f"{animals[0].title()} is a cow.") # in an f-string

Modify, add, insert elements

animals[3] = 'veau'      # replace item 3
animals.append('croc')   # add new item to end of list
animals.insert(1,'pato') # insert item at index 1

Remove elements

del animals[0]                 # delete item at index 0
popped_animal = animals.pop()  # remove last item
popped_animal = animals.pop(2) # remove item at index 2
animals.remove('veau')         # remove (first instance of) item by value

Organize Lists

animals.sort()             # sort values a-z
animals.sort(reverse=True) # sort values z-a
animals.reverse()          # reverse order (not z-a)
print(sorted(animals))     # temporarily sort
len(animals)               # returns number of items

Loop on a List

for animal in animals:                    # for loop requires a colon
    print(animal)                         # indent each line in the loop
    print(f"Hello {animal.title()}")
print(f"We have {len(animals)} animals!") # stop indenting after the loop

Create a list of numbers and list statistics

numbers = list(range(1,11)) # list function makes a list, range function creates 1-10
odd_numbers = list(range(1, 11, 2)) #third parameter is step
even_numbers = list(range(2, 11, 2))

square_numbers = []
for value in range(1, 11):
    square_numbers.append(value ** 2)
    print(square_numbers)

square_nos = [value ** 2 for value in range(1, 11)] # list comprehension
print(square_nos)
print(min(square_nos))
print(max(square_nos))
print(sum(square_nos))

Slice a list

print(square_nos[0:3]) # first three
print(square_nos[2:6]) # 3rd, 4th, 5th, 6th
print(square_nos[:5]) # first five
print(square_nos[5:]) # from 5th to end
print(square_nos[-3:]) # last three
print(square_nos[0:5:2]) # first five, step 2

for number in square_nos[::3]: # every 3rd number of entire list
    print(number)

Copy a list

new_squares = square_nos # new list is linked to old one
new_squares = square_nos[:] # creates a new, separate list

Tuples

Tuples are immutable lists. You cannot modify values in a tuple, but you can replace the entire tuple.

limits = (10, 20) # defines the tuple
limits = (10, 30) # redefines the tuple