How to Convert a List of Lists Into A Single List

Say, you want to convert a list of lists lst=[[1, 2], [3, 4]] into a single list [1, 2, 3, 4]. How to achieve this? There are different options:

Find examples of all three methods in the following code snippet:

lst = [[1, 2], [3, 4]]

# Method 1: List Comprehension
flat_1 = [x for l in lst for x in l]

# Method 2: Unpacking
flat_2 = [*lst[0], *lst[1]]

# Method 3: Extend Method
flat_3 = []
for l in lst:
    flat_3.extend(l)


## Check results:
print(flat_1)
# [1, 2, 3, 4]

print(flat_2)
# [1, 2, 3, 4]

print(flat_3)
# [1, 2, 3, 4]

Due its simplicity and efficiency, the first list comprehension method is superior to the other two methods.

You can check out these methods yourself in our interactive code shell:

Do you need to dive even deeper into this code snippet? Try the Python teacher code execution to see the memory objects created by this code:

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