Nauč se Python > Materiály > Snake Workshop for PyLadies > Introduction to Python > Tuples and unpacking

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N-tuple #

Do you already know that you can return a value from a function using the return statement?

def double(x):
    return x * 2

But how to write a function that returns two values? For example, I want to write a function that calculates the quotient and remainder after division.

Two values can be returned as a list.

def quotient_and_remainder(a, b):
    quotient = a // b
    remainder = a % b

    return [quotient, remainder]

print(quotient_and_remainder(5, 2))

But it's better to return a pair of numbers - two numbers separated by a comma.

def quotient_and_remainder(a, b):
    quotient = a // b
    remainder = a % b

    return quotient, remainder

print(quotient_and_remainder(5, 2))

This is called a pair - and similarly, a trio, quartet, quintet, sextet, simply an n-tuple of values is formed. It works similarly to a list, but it cannot be changed - for example, additional elements cannot be added to it using append. When I have a trio, it always remains as a trio.

When you have an n-tuple, you can unpack it by assigning it to several variables.

quotient, remainder = quotient_and_remainder(5, 2)


N-tuples have many uses, for example:

  • A point in space has 3 coordinates - a triple of numbers!
  • A playing card has a color and a value - a pair of numbers and strings, for example (2, 'spades').

Sometimes it is necessary to add an n-tuple to a list, for example, to save information about a whole pack of playing cards. In similar cases, it is necessary to enclose each n-tuple in parentheses to make it clear where it begins and ends. Here is a list of pairs:

hand = [(2, 'spades'), (10, 'clubs'), (8, 'diamonds')]

When you have such a list, you can go through it in a for loop using unpacking.

for value, color in hand:
    print('I am playing', value, 'and they are', color)

Zip #

The function zip returns an N-tuple or a sequence of n-tuples, which allows you to iterate through multiple lists simultaneously, where the elements correspond to each other.

Items = ['grass', 'sun', 'carrot', 'river']
Colors = ['green', 'yellow', 'orange', 'blue']
Places = ['on the ground', 'up high', 'on the plate', 'behind the wall']

for item, color, place in zip(items, colors, places):
    print(color, item, 'is', place)

In this cycle, you will first receive a trio of the first elements from all three lists, then a trio of all second elements, then third, and so on.

Summary #

What did you learn this time?

  • Using a n-tuple, several values can be combined into one.
  • N-tuples can be unpacked into several variables.
  • The zip function returns a sequence of n-tuples, in which the elements come from several lists.

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