Creating list of lists, with objects from lists

[deanhystad]

You can use zip. Zip is one of my favorite Python functions. I use it all the time.

https://docs.python.org/3/library/functions.html#zip

In the code below I use zip and a list comprehension to make a list of lists.

numbers = ["1", "2", "3", "5"]
letters = ["a", "b", "c", "d", "e"]

pairs = [[letter, number] for letter, number in zip(letters, numbers)]
print(pairs)

Output:
[['a', '1'], ['b', '2'], ['c', '3'], ['d', '5']]

if you don't understand how a list comprehension works, this is the list code written using a for loop.

pairs = []
for letter, number in zip(letters, numbers):
    pairs.append([letter, number])
print(pairs)

Output:
[['a', '1'], ['b', '2'], ['c', '3'], ['d', '5']]

You can also use the built-in list() function.

pairs = list(zip(letters, numbers))

Output:
[('a', '1'), ('b', '2'), ('c', '3'), ('d', '5')]

Notice that list() makes tuples instead of lists. A tuple is like a list, but you can't modify the contents of a tuple. However, tuples have an advantage in speed and memory usage.

And finally I pair up letters and numbers in a dictionary. You may have a good reason for making lists of lists (or tuples), but you should consider using a dictionary.

pairs = dict(zip(letters, numbers))

Output:
{'a': '1', 'b': '2', 'c': '3', 'd': '5'}