Tuples

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Aliasing

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What Is It?

The association of a variable with an object is called a reference.
When there are two (or more) references to the same object, we say that the object is aliased.

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Example

a = [1, 2, 3]
b = a
b is a
# True

b[0] = 7
b
# [7, 2, 3]
a
# [7, 2, 3]

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Tuples

Part 1

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What Is It?

A tuple is a sequence of values.
Tuples are immutable.
Items in a tuple can be any type.

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Creating A Tuple

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Comma Separated List Of Values

t1 = 1, 2, 3, 4, 5
print(t1)
# (1, 2, 3, 4, 5)
type(t1)
# <class 'tuple'>

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Single Element Tuples

When creating a tuple with a single element, you have to include a final comma.

t1 = 'a'
type(t1)
# <class 'str'>

t1 = 'a',
type(t1)
# <class 'tuple'>
print(t1)
# ('a',)

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Enclosed In Parantheses

t2 = ('a', 'e', 'i', 'o', 'u')
print(t2)
# ('a', 'e', 'i', 'o', 'u')
type(t2)
# <class 'tuple'>

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tuple Function

Any sequence or iterator can be converted into a tuple by invoking the tuple function.

t3 = tuple(['king', 'queen', 'bishop', 'knight', 'rook', 'pawn'])
print(t3)
# ('king', 'queen', 'bishop', 'knight', 'rook', 'pawn')
type(t3)
# <class 'tuple'>

name_tuple = tuple("Roberto")
print(name_tuple)
# ('R', 'o', 'b', 'e', 'r', 't', 'o')

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Nested Tuples

Tuples can be nested. In other words, it is possible to create a tuple of tuples.

nested_tuple = (1, 2, 3), (4, 5)
nested_tuple
# ((1, 2, 3), (4, 5))

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Tuples

Part 2

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Accessing Elements From A Tuple

Elements can be accessed with square brackets []. Sequences are 0-indexed.

regular_tuple = (1, 2, 3)
regular_tuple[0]
# 1

nested_tuple = (1, 2, 3), (4, 5)
nested_tuple[1]
# (4, 5)

nested_tuple[1][0]
# 4

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Tuples Are Immutable

sides = ('a', 'b')
sides[0] = 'z'
# Traceback (most recent call last):
#   File "<stdin>", line 1, in <module>
# TypeError: 'tuple' object does not support item assignment

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Mutable Objects Inside Of Tuples

If an object inside of a tuple is mutable, you can modify it in place

my_tuple = (['a', 'b', 'c'], 'roberto', (1, 2, 3))
my_tuple[0]
# ['a', 'b', 'c']
 my_tuple[0].append('d')
my_tuple[0]
(['a', 'b', 'c', 'd'], 'roberto', (1, 2, 3))

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Tuple Concatenation

fruits = ('apples', 'bananas')
vegetables = ('green beans', 'broccoli')
fruits + vegetables
# ('apples', 'bananas', 'green beans', 'broccoli')

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Tuples

Part 3

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Unpacking Tuples

nums_tup = (1, 2, 3)
a, b, c = nums_tup
a
# 1
b 
# 2
c 
# 3

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Tuple Assignment

Suppose you needed to swap the values of variables a and b. A conventional solution would involve assigning one of the values to a temporary variable.

a = 1
b = 2
print(a, b)
# (1, 2)

temp = a
a = b
b = temp
print(a, b)
# (2, 1)

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Tuple Assignment

The left side is a tuple of variables.
The right side is a tuple of expressions.
Each value is assigned to its respective variable.
All the expressions on the right side are evaluated before any of the assignments.
The number of variables on the left and the number of values on the right have to be the same.

a = 1
b = 2
print(a, b)
# (1, 2)
a, b = b, a
print(a, b)
# (2, 1)

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Tuples As Return Values

A function can only return one value.
A tuple can be used to effectively return multiple values.

def first_and_last(word):
    return word[0], word[-1]

print(first_and_last("monkey"))
# ('m', 'y')

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Tuples As Args - Gather

Functions can take a variable number of arguments. A parameter name that begins with * gathers positional arguments into a tuple.

def print_all(*args):
    print(type(args))
    for item in args:
        print(item)

print_all("kit kat", "snickers", "milky way")
# <class 'tuple'>
# kit kat
# snickers
# milky way

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Tuples As Args - Scatter

def sum(a, b):
    return a + b

print(sum(1, 2))
# 3

t = (1, 2)
print(sum(*t))
# 3

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Tuple Methods - count

name = tuple('roberto')
name.count('o')
# 2

customer_age = (18, 18, 19, 21, 21, 25, 30, 55)
customer_age.count(18)
# 2

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zip Built-in Function

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What Is It?

A function that takes two or more sequences and interleaves them.
Returns a zip object.

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How Does It Work?

s = 'abc'
t = [0, 1, 2]
result = zip(s, t)
type(result)
# <class 'zip'>
print(result)
# <zip object at 0x10b7c2188>

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Special Note About Python 2

In Python 2, the zip function returns a list of tuples.

s = 'abc'
t = [0, 1, 2]
zip(s, t)
# [('a', 0), ('b', 1), ('c', 2)]
result = zip(s, t)
type(result)
# <type 'list'>

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Iterating With Zip

s = 'abc'
t = [0, 1, 2]
for pair in zip(s, t):
    print(pair)

# ('a', 0)
# ('b', 1)
# ('c', 2)

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enumerate Built-in Function

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What is it?

A function that takes an interable and allows the iteration over a sequence of pairs; an index and an element from the given iterable.
Returns an enumerate object.

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How Does It Work?

trilogy = ['The Matrix', 'The Matrix Reloaded', 'The Matrix Revolutions']
for index, element in enumerate(trilogy, start= 1):
    print(index, element)

# 1 The Matrix
# 2 The Matrix Reloaded
# 3 The Matrix Revolutions

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The End

Parrot