💬 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
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) # [, [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) # [, [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 function 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
tuples = ((1,), (2, 3, 4), (5, 6, 7, 8)) lists = list(map(list, tuples)) print(lists) # [, [2, 3, 4], [5, 6, 7, 8]]
Try it yourself:
Video tutorial on the
The first argument of the
map() function is the
list function name.
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) # [, [2, 3, 4], [5, 6, 7, 8]]
Related Video Tutorial
Related Conversion Articles
- How to Convert a List of Lists to a List of Tuples
- How to Convert a List of Lists to a Pandas Dataframe
- How to Convert a List of Lists to a NumPy Array
- How to Convert a List of Lists to a Dictionary in Python
Where to Go From Here?
Enough theory. Let’s get some practice!
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While working as a researcher in distributed systems, Dr. Christian Mayer found his love for teaching computer science students.
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