Adding lists to a list

Question

I have a value that creates a list with two values. I need to add it as a sublist to another list muptiple times.

I need the resulting list to look like this: [["a", 1], ["b", 2], ["c", 3], ["d", 4]]

So this:

Small_list = []
Big_list = []
for item in db[1:]:
   Small_list.append(item)
   for item2 in db[2:]:
      Small_list.append(item2)
      Big list.append()
print(Big_list)

Returns: [[], [], [], []]

But doing the .extend() method

Small_list = []
Big_list = []
for item in db[1:]:
   Small_list.append(item)
   for item2 in db[2:]:
      Small_list.append(item2)
      Big list.extend()
print(Big_list)

Returns: ["a", 1, "b", 2, "c", 3, "d", 4]

Why does this happen and how do I do it the right way?

Are you sure your two examples are actually exactly what you are running? In both cases, nothing should be getting added into Big_list as both the append and extend list methods require you to pass them values, which is not being done in either or your cases. — Matt Pitkin
– Matt Pitkin, Commented Dec 13, 2024 at 10:52
Please also provide information on what db contains, so that your question is reproducible. — Matt Pitkin
– Matt Pitkin, Commented Dec 13, 2024 at 10:55
It's a list of lists containing data from google spreadsheets through gspread's worksheet.get_all_values() — Crip
– Crip, Commented Dec 13, 2024 at 11:23

Snoke · Accepted Answer · 2024-12-13 10:55:39Z

0

The Small_list is not getting reset.

The .extend() adds content to the end of the list.

In order for this to work:

Create a new Small_list for every pair of values.
Append the Small_list to Big_list.

Example Code:

db = ["a", 1, "b", 2, "c", 3, "d", 4]  # Example data
Big_list = []

# Assuming `db` contains alternating elements (key-value pairs)
for i in range(0, len(db), 2):  # Step by 2 to process pairs
    Small_list = [db[i], db[i + 1]]  # Create a new sublist for each pair
    Big_list.append(Small_list)  # Add the sublist to the big list

print(Big_list)

answered Dec 13, 2024 at 10:55

Snoke

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4 Comments

Crip Dec 13, 2024 at 11:05

My fault, I forgot to mention that I do Small_list.clear() at the end of the second for loop I'm just curious as to why it doesn't pass any values within lists, while a "print" would show [a, 1], [b, 2] and so on for every loop

Crip Dec 13, 2024 at 11:06

Oh, and db itself contains a list of lists, it's just rows from a google spreadsheet basically

Snoke Dec 13, 2024 at 11:30

When you call Small_list.clear(), you're emptying the same list object that Big_list references.

Snoke Dec 13, 2024 at 11:35

What does your db look like?

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