Python Unpacking Tuple

Summary: in this tutorial, you’ll learn how to unpack tuples in Python.

Reviewing Python tuples #

Python defines a tuple using commas (,), not parentheses (). For example, the following defines a tuple with two elements:

1,2Copy

Python uses the parentheses to make the tuple clearer:

(1, 2)Copy

Python also uses the parentheses to create an empty tuple:

()Copy

In addition, you can use the tuple() constructor like this:

tuple()Copy

To define a tuple with only one element, you still need to use a comma. The following example illustrates how to define a tuple with one element:

1,Copy

It’s equivalent to the following:

(1, )Copy

Note that the following is an integer, not a tuple:

(1)Copy

Unpacking a tuple #

Unpacking a tuple means splitting the tuple’s elements into individual variables. For example:

x, y = (1, 2)Copy

The left side:

x, yCopy

is a tuple of two variables x and y.

The right side is also a tuple of two integers 1 and 2.

The expression assigns the tuple elements on the right side (1, 2) to each variable on the left side (x, y) based on the relative position of each element.

In the above example, x will take 1 and y will take 2.

See another example:

x, y ,z = 10, 20, 30Copy

The right side is a tuple of three integers 10, 20, and 30. You can quickly check its type as follows:

numbers = 10, 20, 30
print(type(numbers))Copy

Try it

Output:

<class 'tuple'>Copy

In the above example, the x, y, and z variables will take the values 10, 20, and 30 respectively.

Using unpacking tuple to swap values of two variables #

Traditionally, to swap the values of two variables, you would use a temporary variable like this:

x = 10
y = 20

print(f'x={x}, y={y}')

tmp = x
x = y
y = tmp

print(f'x={x}, y={y}')Copy

Try it

Output:

x=10, y=20
x=20, y=10Copy

In Python, you can use the unpacking tuple syntax to achieve the same result:

x = 10
y = 20

print(f'x={x}, y={y}')

x, y = y, x

print(f'x={x}, y={y}')Copy

Try it

Output:

x=10, y=20
x=20, y=10Copy

The following expression swaps the values of two variables, x and y.

x, y = y, xCopy

In this expression, Python evaluates the right-hand side first and then assigns the variable from the left-hand side to the values from the right-hand side.

ValueError: too many values to unpack #

The following example unpacks the elements of a tuple into variables. However, it’ll result in an error:

x, y = 10, 20, 30Copy

Error:

ValueError: too many values to unpack (expected 2)Copy

This error is because the right-hand side returns three values while the left-hand side only has two variables.

To fix this, you can add a _ variable:

x, y, _ = 10, 20, 30Copy

The _ variable is a regular variable in Python. By convention, it’s called a dummy variable.

Typically, you use the dummy variable to unpack when you don’t care and use its value afterward.

Extended unpacking using the * operator #

Sometimes, you don’t want to unpack every single item in a tuple. For example, you may want to unpack the first and second elements. In this case, you can use the * operator. For example:

r, g, *other = (192, 210, 100, 0.5)Copy

Output:

192
210
[100, 0.5]Copy

In this example, Python assigns 192 to r, 210 to g. Also, Python packs the remaining elements 100 and 0.5 into a list and assigns it to the other variable.

Notice that you can only use the * operator once on the left-hand side of an unpacking assignment.

The following example results in error:

x, y, *z, *t = (10, 20, 30, '10:30')Copy

Error:

SyntaxError: two starred expressions in assignmentCopy

Using the * operator on the right hand side #

Python allows you to use the * operator on the right-hand side. Suppose that you have two tuples:

odd_numbers = (1, 3, 5)
even_numbers = (2, 4, 6)Copy

The following example uses the * operator to unpack those tuples and merge them into a single tuple:

odd_numbers = (1, 3, 5)
even_numbers = (2, 4, 6)

numbers = (*odd_numbers, *even_numbers)
print(numbers)Copy

Try it

Output:

(1, 3, 5, 2, 4, 6)Copy

Summary #

• Python uses the commas (,) to define a tuple, not parentheses.
• Unpacking tuples means assigning individual elements of a tuple to multiple variables.
• Use the * operator to assign remaining elements of an unpacking assignment into a list and assign it to a variable.

Quiz #