Answer: The simplest, most straightforward, and most readable way to convert a tuple to a list is Python’s built-in list(tuple) function. You can pass any iterable (such as a tuple, another list, or a set) as an argument into this so-called constructor function and it returns a new list data structure that contains all elements of the iterable.
Converting a tuple to a list seems trivial, I know. But keep reading and I’ll show you surprising ways of handling this problem. I guarantee that you’ll learn a lot of valuable things from the 3-5 minutes you’ll spend reading this tutorial! 🙂
Problem: Given a tuple of elements. Create a new list with the same elements—thereby converting the tuple to a list.
Example: You have the following tuple.
t = (1, 2, 3)
You want to create a new list data structure that contains the same integer elements:
[1, 2, 3]
Let’s have a look at the different ways to convert a tuple to a list—and discuss which is the most Pythonic way in which circumstance.
You can get a quick overview in the following interactive code shell. Explanations for each method follow after that:
Exercise: Run the code. Skim over each method—which one do you like most? Do you understand each of them?
Let’s dive into the six methods.
Method 1: List Constructor
The simplest, most straightforward, and most readable way to convert a tuple to a list is Python’s built-in list(iterable) function. You can pass any iterable (such as a list, a tuple, or a set) as an argument into this so-called constructor function and it returns a new tuple data structure that contains all elements of the iterable.
Here’s an example:
# Method 1: list() constructor t = (1, 2, 3) lst = list(t) print(lst) # [1, 2, 3]
This is the most Pythonic way if a flat conversion of a single tuple to a list is all you need. But what if you want to convert multiple tuples to a single list?
Method 2: Unpacking
There’s an alternative that works for one or more tuples to convert one or more tuples into a list. This method is equally efficient and it takes less characters than Method 1 (at the costs of readability for beginner coders). Sounds interesting? Let’s dive into unpacking and the asterisk operator!
The asterisk operator * is also called “star operator” and you can use it as a prefix on any tuple (or list). The operator will “unpack” all elements into an outer structure—for example, into an argument lists or into an enclosing container type such as a list or a tuple.
Here’s how it works to unpack all elements of a tuple into an enclosing list—thereby converting the original tuple to a new list.
# Method 2: Unpacking t = (1, 2, 3) lst = [*t] print(lst) # [1, 2, 3]
You unpack all elements in the tuple t into the outer structure [*t]. The strength of this approach is—despite being even conciser than the standard list(...) function—that you can unpack multiple values into it!
Method 3: Unpacking to Convert Multiple Tuples to a Single List
Let’s have a look at how you’d create a list from multiple tuples:
# Method 3: Unpacking Multiple Tuples t1 = (1, 2, 3) t2 = (4, 5, 6) lst = [*t1, *t2] print(lst) # [1, 2, 3, 4, 5, 6]
The expression [*t1, *t2] unpacks all elements in tuples t1 and t2 into the outer list. This allows you to convert multiple tuples to a single list.
Method 4: Generator Expression to Convert Multiple Tuples to List
If you have multiple tuples stored in a list of lists (or list of tuples) and you want to convert them to a single list, you can use a short generator expression statement to go over all inner tuples and over all elements of each inner tuple. Then, you place each of those elements into the list structure:
# Method 4: Generator Expression ts = ((1, 2), (3, 4), (5, 6, 7)) lst = [x for t in ts for x in t] print(lst) # [1, 2, 3, 4, 5, 6, 7]
This is the most Pythonic way to convert a list of tuples (or tuple of tuples) to a tuple. It’s short and efficient and readable. You don’t create any helper data structure that takes space in memory.
But what if you want to save a few more characters?
Method 5: Generator Expression + Unpacking
Okay, you shouldn’t do this last method using the asterisk operator—it’s unreadable—but I couldn’t help including it here:
# Method 5: Generator Expression + Unpacking t = ((1, 2), (3, 4), (5, 6, 7)) lst = [*(x for t in ts for x in t)] print(lst) # [1, 2, 3, 4, 5, 6, 7]
Rather than using the list(...) function to convert the generator expression to a list, you use the [...] helper structure to indicate that it’s a list you want—and unpack all elements from the generator expression into the list. Sure, it’s not very readable—but you could see such a thing in practice (if pro coders want to show off their skills ;)).
Method 6: Simple For Loop
Let’s end this article by showing the simple thing—using a for loop. Doing simple things is an excellent idea in coding. And, while the problem is more elegantly solved in Method 1 (using the list() constructor), using a simple loop to fill an initially empty list is the default strategy.
# Method 6: Simple For Loop
t = (1, 2, 3, 4)
lst = []
for x in t:
lst.append(x)
print(lst)
# [1, 2, 3, 4]To understand how the code works, you can visualize its execution in the interactive memory visualizer:
Exercise: How often is the loop condition checked?
You will see such a simple conversion method in code bases of Python beginners and programmers who switch to Python coming from other programming languages such as Java or C++. It’s readable but it lacks conciseness.
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