# Sequence Data Type

Sequential data types can be used to store an array of values.

For example, if you want to represent all the game titles that you collect, you don't need to create an individual variable for each of your game. You can specify a variable of sequential data type to store all games.

# List

list is a primitive sequential data type in Python.

To create a list variable for our games,

games = [
    "Fortnite",
    "Minecraft",
    "Grand Theft Auto V",
    "The Legend of Zelda",
    "Pokemon",
]

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A pair of [] denotes a list. It can hold various values. In the example above, games is a list that holds some strings.

# access values in the list

We can access each of the values stored in a list by its index. Again, Python follows 0-indexed, meaning indices start with 0.

The first item of a list has index of 0. The n-th item of a list has index of n-1.

print(games[0])
print(games[2])

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Python also supports negative index. -1 refers to the last item, -2 refers to the second last item, so on and so forth.

print(games[-1])
print(games[-3])

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We can not only read values from a list but also modify them.

games[2] = "Grand Theft Auto VI"
games[-1] = "Pokemon Go"
print(games)

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# built-in functions for list

We can use len() to get the length of a list, a.k.a. the number of items in that list.

print(len(games))

If we have a list of numbers, there are handy built-in functions to get simple statistics.

For example, we have

numbers = [1, 2, 3, 4.5, 6, 7.8, 9, 10]

We can use max(), min(), and sum() to get the largest number, smallest number, and summation of all numbers, respectively.

print(max(numbers))
print(min(numbers))
print(sum(numbers))

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# operators for list

+ would concat two lists together

a = [1, 2, 3]
b = [4, 5, 6]

print(a + b)

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* would duplicate the list for a given amount of times

a = ["a", "b", "c"]

print(a * 3)

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# functions of list

list also comes with functions and attributes. To access them, we use the . to access its own functions/attributes.

games.reverse()
print(games)

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reverse() is a general function of list that reverse the order of all items in it.

We use append() to add an item at the end of a list.

games.append("Super Smash Bros.")
print(games)

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We use extend() to add more items at the end of a list, where you put those items in a list.

games.extend(["FIFA 20", "Plants vs. Zombies"])
print(games)

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We use clear() to empty all items from the list.

games.clear()
print(games)

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We use remove() to delete the first match of an item from the list.

games.remove("The Legend of Zelda")
print(games)

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l = [1, 2, 3] * 2
l.remove(3)
print(l)

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We use pop() to delete the last item from the list.

animals = ['cat', 'dog', 'rabbit', 'guinea pig']
animals.pop()
print(animals)

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We use insert() to add item at a given location of the list.

animals.insert(0, "guinea pig")
print(animals)

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We use index() to get the index of the first match of an item in the list.

print(animals.index("cat"))

print((animals * 3).index("cat"))

We use count() to get number of times the an element appears in the list.

print(animals.count("cat"))

print((animals * 3).count("cat"))

# list comprehension

To get all letters in a string and store them in a list

letters = []

for letter in "learn Python":
    letters.append(letter)

print(letters)

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A more Pythonic way to achieve this task is as follow.

letters = [letter for letter in "learn Python"]

print(letters)

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To get all non-vowel letters in the string

letters = [letter for letter in "learn Python" if letter not in "aeiou"]

print(letters)

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To get all odd numbers from 1 to 100

print([i for i in range(1, 101) if i % 2])

To multiply all numbers by 5 in the list

print([i * 5 for i in range(1, 101)])

# Tuple

tuple is very similar with list except that the items in the tuple cannot be changed.

To create a tuple variable we use a pair of ()

awesome_collection = (
    "Fortnite",
    "Minecraft",
    "Grand Theft Auto V",
    "The Legend of Zelda",
    "Pokemon",
)

print(len(awesome_collection))
print(awesome_collection[1])
print(awesome_collection[-1])
print(awesome_collection + ("Mario",))
print(awesome_collection * 2)

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However, Python would throw an error (TypeError: 'tuple' object does not support item assignment) if we try to modify the item in the tuple.

awesome_collection[0]="NBA 2K21"

# functions of tuple

We can dir() to list all attributes and functions of a specified object. See what's available for tuple.

# Assignment 10

Create a Python script named score_keeper.py that would prompt the user for the number of scores it's going to keep. Then it asks the user to enter a numeric value score for that given number of times. Finally it displays the average of of the scores.

Please use list in the solution. A sample run looks like the following.

python score_keeper.py
Enter number of scores: 3
Enter score: 100
Enter score: 99
Enter score: 60
Average score is 86.33333333333333

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Sample Solution

size = int(input("Enter number of scores: "))

scores = []
for i in range(size):
    score = float(input("Enter score: "))
    scores.append(score)

print("Average score is", sum(scores) / size)

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