Tuples

Container Types

• Strings contain a sequence of characters
• Lists contain a sequence of values of any type
• Dictionaries contain values of any type indexed by key

Tuples

• Tuples contain a sequence of values
• Values may be any type

Tuple Creation

• Tuples are created as comma-separated values

Example

t = 1, 2

print(t)

Small Tuples

• A one-item tuple can be created using a trailing comma t = 1,
• An empty tuple may be created using the tuple constructor or empty parens (())

Example

single = "a",
print(single)

empty = tuple()
print(empty)

empty = ()
print(empty)

Tuple constructor

• The tuple constructor can also be used to convert other types into tuples

Example

letters = tuple("Hello")

print(letters)

Tuple Features

• Indexing works like lists for the most part
• Assigning via index is not allowed (like strings)

Example

t = "a", "b", "c"

print(t[1])

t[1] = "x"

Immutability

• The container itself is immutable
• Mutable values (such as lists) can still be modified

Example

t = ("A", [1, 2])

print(t)

t[1].append(3)

print(t)

Destructuring Assignment

• A destructuring assignment can be used to assign multiple values at once
• The right hand side must be the same length as the left hand side

Example

a, b = (1, 2)

print(a)
print(b)

Example

word1, word2 = "Hello world".split()

print(word1)
print(word2)

Exercise

Write a concise program to swap the values in two variables, a and b

Tuple Comparison

• Tuples are compared one element at a time (like strings)
• Once a larger element is found, that tuple is considered to larger
  • Future elements are not considered

Example

smaller = (1, 3, 1000)
larger = (1, 4, 0)

print(smaller < larger)

DSU Pattern

• Uses tuples for sorting items
• Decorate items using a sort key
• Sort items
• Undecorate the items by removing the sort key

Exercise

Write a Python program that creates a list of all words in a sentence. The list should be sorted by the length of the word, smallest first. For example, the sentence “She is a girl” should produce:

['a', 'is', 'She', 'girl']

Solution

sentence = "The quick brown fox jumped over the lazy dog"

decorated = []

for word in sentence.split():
    decorated.append((len(word), word))

decorated.sort()

undecorated = []

for _, word in decorated:
    undecorated.append(word)

print(undecorated)