[Tut] How to Convert List of Lists to Tuple of Tuples in Python?

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

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Question: Given a list of lists such as

Code:

[[1, 2], [3, 4]]

. How to convert it to a tuple of tuples such as

Code:

((1, 2), (3, 4))

?

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

Use a generator expression with the built-in

Code:

tuple()

function to convert a list of lists to a tuple of tuples like so:

Code:

tuple(tuple(x) for x in my_list)

.

Here’s a graphic on how to convert back and forth between nested list and nested tuples:



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: Tuple Comprehension + tuple()

The recommended way to convert a list of lists to a tuple of tuples is using generator expression in combination with the built-in

Code:

tuple()

function like so:

Code:

tuple(tuple(x) for x in my_list)

.

Here’s a concrete example:

Code:

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

Try It Yourself:

https://trinket.io/embed/python/98fd39ea7a

This approach is simple and effective. The generator expression defines how to convert each inner list (

Code:

x

in the example) to a new tuple element.

You use the constructor

Code:

tuple(x)

to create a new tuple from the list

Code:

x

.



Example Three Elements per Tuple

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

Code:

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

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

https://pythontutor.com/iframe-embed.htm...nces=false

Example Varying Number of List Elements

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

Code:

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

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

But are there any alternatives? Let’s have a look at a completely different approach to solve this problem:

Method 2: 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

Code:

map()

function as it’s less readable and less efficient than the generator expression 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 list of lists into a tuple of tuples using the

Code:

map()

function:

Code:

lists = [[1], [2, 4, 3], [6, 5]] tuples = tuple(map(tuple, lists)) print(tuples) # ((1,), (2, 4, 3), (6, 5))

Try it yourself:

https://trinket.io/embed/python/988e6b062f

Video tutorial on the

Code:

map()

function:



The first argument of the

Code:

map()

function is the

Code:

tuple

function name.

This

Code:

tuple()

function converts each element on the given iterable

Code:

lists

(the second argument) into a tuple.

The result of the

Code:

map()

function is an iterable too, so you need to convert it to a tuple before printing it to the shell because the default string representation of an iterable is not human-readable.

Method 3: Simple For Loop with append() and tuple()

To convert a list of lists to a tuple of tuples, first initialize an empty “outer” list and store it in a variable.

Then iterate over all lists using a simple

Code:

for

loop and convert each separately to a tuple.

Next, append each result to the outer list variable using the

Code:

list.append()

builtin method in the loop body.

Finally, convert the list of tuples to a list tuple of tuples using the

Code:

tuple()

function.

The following example does exactly that:

Code:

lists = [[1], [2, 4, 3], [6, 5]] tmp = [] for t in lists: tmp.append(tuple(t)) tuples = tuple(tmp) print(tuples) # ((1,), (2, 4, 3), (6, 5))

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
  
  
• https://blog.finxter.com/how-to-convert-...mpy-array/How to Convert a List of Lists to a NumPy Array
  
  
• How to Convert a List of Lists to a Dictionary in Python
  
  
• How to Convert a Tuple of Tuples to a List of Lists in Python
  

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