Python Tuple

What is Python Tuple?

A tuple is an ordered collection of values.

Tuples are a lot like lists:

• Tuples are ordered – Tuples maintains a left-to-right positional ordering among the items they contain.
• Accessed by index – Items in a tuple can be accessed using an index.
• Tuples can contain any sort of object – It can be numbers, strings, lists and even other tuples.

except:

• Tuples are immutable – you can’t add, delete, or change items after the tuple is defined.

Create a Tuple

You can create a tuple by placing a comma-separated sequence of items in parentheses ().

# A tuple of integers
T = (1, 2, 3)

# A tuple of strings
T = ('red', 'green', 'blue')

The items of a tuple don’t have to be the same type. The following tuple contains an integer, a string, a float, and a boolean.

# A tuple with mixed datatypes
T = (1, 'abc', 1.23, True)

A tuple containing zero items is called an empty tuple and you can create one with empty
brackets ()

# An empty tuple
T = ()

Syntactically, a tuple is just a comma-separated list of values.

# A tuple without parentheses
T = 1, 'abc', 1.23, True

You don’t need the parentheses to create a tuple. It’s the trailing commas that really define a tuple. But using them doesn’t hurt; also they help make the tuple more visible.

Singleton Tuple

If you have only one value in a tuple, you can indicate this by including a trailing comma , just before the closing parentheses.

T = (4,)
print(type(T))
# Prints <type 'tuple'>

Otherwise, Python will think you’ve just typed a value inside regular parentheses.

# Not a tuple
T = (4)
print(type(T))
# Prints <type 'int'>

The tuple() Constructor

You can convert other data types to tuple using Python’s tuple() constructor.

# Convert a list to a tuple
T = tuple([1, 2, 3])
print(T)
# Prints (1, 2, 3)

# Convert a string to a tuple
T = tuple('abc')
print(T)
# Prints ('a', 'b', 'c')

Nested Tuples

A tuple can contain sub-tuple, which in turn can contain sub-tuples themselves, and so on. This is known as nested tuple. You can use them to arrange data into hierarchical structures.

T = ('red', ('green', 'blue'), 'yellow')

Tuple Packing & Unpacking

Tuple Packing

When a tuple is created, the items in the tuple are packed together into the object.

T = ('red', 'green', 'blue', 'cyan')
print(T)
# Prints ('red', 'green', 'blue', 'cyan')

In above example, the values ‘red’, ‘green’, ‘blue’ and ‘cyan’ are packed together in a tuple.

Tuple Unpacking

When a packed tuple is assigned to a new tuple, the individual items are unpacked (assigned to the items of a new tuple).

T = ('red', 'green', 'blue', 'cyan')
(a, b, c, d) = T

print(a)
# Prints red

print(b)
# Prints green

print(c)
# Prints blue

print(d)
# Prints cyan

In above example, the tuple T is unpacked into a, b, c and d variables.

When unpacking, the number of variables on the left must match the number of items in the tuple.

# Common errors in tuple unpacking

T = ('red', 'green', 'blue', 'cyan')
(a, b) = T
# Triggers ValueError: too many values to unpack

T = ('red', 'green', 'blue')
(a, b, c, d) = T
# Triggers ValueError: not enough values to unpack (expected 4, got 3)

Usage

Tuple unpacking comes handy when you want to swap values of two variables without using a temporary variable.

# Swap values of 'a' and 'b'
a = 1
b = 99

a, b = b, a

print(a)
# Prints 99

print(b)
# Prints 1

While unpacking a tuple, the right side can be any kind of sequence (tuple, string or list).

# Split an email address into a user name and a domain
addr = 'bob@python.org'
user, domain = addr.split('@')

print(user)
# Prints bob

print(domain)
# Prints python.org

Access Tuple Items

You can access individual items in a tuple using an index in square brackets. Note that tuple indexing starts from 0.

The indices for the elements in a tuple are illustrated as below:

T = ('red', 'green', 'blue', 'yellow', 'black')

print(T[0])
# Prints red

print(T[2])
# Prints blue

You can access a tuple by negative indexing as well. Negative indexes count backward from the end of the tuple. So, T[-1] refers to the last item, T[-2] is the second-last, and so on.

T = ('red', 'green', 'blue', 'yellow', 'black')

print(T[-1])
# Prints black

print(T[-2])
# Prints yellow

Tuple Slicing

To access a range of items in a tuple, you need to slice a tuple using a slicing operator. Tuple slicing is similar to list slicing.

T = ('a', 'b', 'c', 'd', 'e', 'f')

print(T[2:5])
# Prints ('c', 'd', 'e')

print(T[0:2])
# Prints ('a', 'b')

print(T[3:-1])
# Prints ('d', 'e')

Change Tuple Items

Tuples are immutable (unchangeable). Once a tuple is created, it cannot be modified.

T = ('red', 'green', 'blue')
T[0] = 'black'
# Triggers TypeError: 'tuple' object does not support item assignment

The tuple immutability is applicable only to the top level of the tuple itself, not to its contents. For example, a list inside a tuple can be changed as usual.

T = (1, [2, 3], 4)
T[1][0] = 'xx'
print(T)
# Prints (1, ['xx', 3], 4)

Delete a Tuple

Tuples cannot be modified, so obviously you cannot delete any item from it. However, you can delete the tuple completely with del keyword.

T = ('red', 'green', 'blue')
del T

Tuple Concatenation & Repetition

Tuples can be joined using the concatenation operator + or Replication operator *

# Concatenate
T = ('red', 'green', 'blue') + (1, 2, 3)
print(T)
# Prints ('red', 'green', 'blue', 1, 2, 3)

# Replicate
T = ('red',) * 3
print(T)
# Prints ('red', 'red', 'red')

Find Tuple Length

To find how many items a tuple has, use len() method.

T = ('red', 'green', 'blue')
print(len(T))
# Prints 3

Check if item exists in a tuple

To determine whether a value is or isn’t in a tuple, you can use in and not in operators with if statement.

# Check for presence
T = ('red', 'green', 'blue')
if 'red' in T:
    print('yes')

# Check for absence
T = ('red', 'green', 'blue')
if 'yellow' not in T:
    print('yes')

Iterate through a tuple

To iterate over the items of a tuple, use a simple for loop.

T = ('red', 'green', 'blue')
for item in T:
    print(item)
# Prints red green blue

Tuple Sorting

There are two methods to sort a tuple.

Method 1: Use the built-in sorted() method that accepts any sequence object.

T = ('cc', 'aa', 'dd', 'bb')
print(tuple(sorted(T)))
# Prints ('aa', 'bb', 'cc', 'dd')

Method 2: Convert a tuple to a mutable object like list (using list constructor), gain access to a sorting method call (sort()) and convert it back to tuple.

T = ('cc', 'aa', 'dd', 'bb')
tmp = list(T)    # convert tuple to list
tmp.sort()       # sort list
T = tuple(tmp)   # convert list to tuple
print(T)         # Prints ('aa', 'bb', 'cc', 'dd')

Python Tuple Methods

Python has a set of built-in methods that you can call on tuple objects.

Built-in Functions with Tuple

Python also has a set of built-in functions that you can use with tuple objects.