How to Convert Tuple of Tuples to List of Lists in Python?

💬 Question: Given a tuple of tuples such as ((1, 2), (3, 4)). How to convert it to a list of lists such as [[1, 2], [3, 4]]?

If you’re in a hurry, here’s the most Pythonic way to convert a nested tuple to a nested list:

The list comprehension statement [list(x) for x in tuples] converts each tuple in tuples to a list and stores the results in a list of lists.

But there’s more to it! Studying the different methods to achieve the same goal will make you a better coder.

So keep reading!

Method 1: List Comprehension + list()

The recommended way to convert a tuple of tuples to a list of lists is using list comprehension in combination with the built-in list() function like so: [list(x) for x in tuples].

Here’s a concrete example:

tuples = ((1, 2), (3, 4), (5, 6))
lists = [list(x) for x in tuples]

print(lists)
# [[1, 2], [3, 4], [5, 6]]

Try It Yourself:

This approach is simple and effective. List comprehension defines how to convert each tuple (x in the example) to a new list element. As each list element is a new list, you use the constructor list(x) to create a new list from the tuple x.

Example Three Elements per Tuple

If you have three elements per tuple, you can use the same approach with the conversion:

tuples = ((1, 2, 1), (3, 4, 3), (5, 6, 5))
lists = [list(x) for x in tuples]
print(lists)

You can see the execution flow in the following interactive visualization (just click the “Next” button to see what’s happening in the code):

Example Varying Number of Tuple Elements

And if you have a varying number of elements per tuple, this approach still works beautifully:

tuples = ((1,), (3, 3), (5, 6, 5))
lists = [list(x) for x in tuples]

print(lists)
# [[1], [3, 3], [5, 6, 5]]

You see that an approach with list comprehension is the best way to convert a tuple of tuples to a list of lists.

But are there any alternatives?

Method 2: Use Asterisk and List Comprehension

A variant of the recommended way to convert a tuple of tuples to a list of lists is using list comprehension in combination with the unpacking asterisk operator * like so: [[*x] for x in tuples].

Here’s an example:

tuples = ((1,), (3, 3), (5, 6, 5))
lists = [[*x] for x in tuples]

print(lists)
# [[1], [3, 3], [5, 6, 5]]

The unpacking operator [*x] takes all tuple elements from x and “unpacks” them in the outer list container [...]. For example, the expression [*(5, 6, 5)] yields the list [5, 6, 5].

Let’s have a look at a completely different approach to solve this problem:

Method 3: Map Function + list()

Use the map fu n ction that applies a specified function on each element of an iterable.

💡Side Note: Guido van Rossum, the creator of Python, didn’t like the map() function as it’s less readable and less efficient than the list comprehension version (Method 1 in this tutorial). You can read about a detailed discussion on how exactly he argued on my blog article.

So, without further ado, here’s how you can convert a tuple of tuples into a list ot lists using the map() function:

tuples = ((1,), (2, 3, 4), (5, 6, 7, 8))
lists = list(map(list, tuples))

print(lists)
# [[1], [2, 3, 4], [5, 6, 7, 8]]

Try it yourself:

Video tutorial on the map() function:

The first argument of the map() function is the list function name.

This list() function converts each element on the given iterable tuples (the second argument) into a list.

The result of the map() function is an iterable too, so you need to convert it to a list before printing it to the shell because the default string representation of an iterable is not human-readable.

Method 4: Simple For Loop with append() and list()

To convert a tuple of tuples to a list of lists, a simple three-liner is to first initialize an empty “outer” list and store it in a variable. Then iterate over all tuples using a simple for loop and convert each separately to a list and append each result to the outer list variable using the list.append() builtin method in the loop body.

The following example does exactly that:

tuples = ((1,), (2, 3, 4), (5, 6, 7, 8))

lists = []
for t in tuples:
    lists.append(list(t))

print(lists)
# [[1], [2, 3, 4], [5, 6, 7, 8]]

Where to Go From Here?

Enough theory. Let’s get some practice!

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