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:
- List comprehension
[x for l in lst for x in l]assuming you have a list of lists
[*lst, *lst]assuming you have a list of two lists
- Using the
extend()method of Python lists to extend all lists in the list of lists.
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, *lst] # 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:
Where to Go From Here?
Enough theory. Let’s get some practice!
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