Removing a list from a list

You don't have to have an else block, especially if all it will contain is pass.

The real reason your code doesn't work is because when you delete items from a list that you're looping through, it doesn't recalculate the length or the current index, so you kind of 'skip' items.

To see what is happening, add a print(type(item), item) to the start of your loop:

>>> the_list = ["a", 2, 3, 1, False, [1, 2, 3]]
>>>
>>> for item in the_list:
...     print(type(item), item)
...     if isinstance(item, str):
...         del the_list[the_list.index(item)]
...     elif isinstance(item, bool):
...         del the_list[the_list.index(item)]
...     elif isinstance(item, list):
...         del the_list[the_list.index(item)]
...
<class 'str'> a
<class 'int'> 3
<class 'int'> 1
<class 'bool'> False

As you can see, it prints the string a right at the beginning. Then it deletes that item from the list, and then moves to the item at index 1, which is now the integer 3. It prints that, moves on, prints the integer 1, moves on, prints the boolean False, deletes it, tries to move to the item at index 5, but realises it has reached the end of the list (because you now only have 4 items), so it exits the loop.

In the first lot of code you shared, it would do another loop based on the list with 4 items, and not finding any strings or booleans, would successfully delete the list.

To get around this behaviour, you could either create a new list of the items you want to keep and just reassign the value of the_list to it, use a counter variable and a while loop and decrement it when you delete something so it doesn't skip items, filter the list and reassign the results to the original, or loop over a copy of the list.

I would suggest the last option, as it is the easiest (though if you had a very large list, probably not the most efficient). Note the slice syntax [:], which just means every item in the list:

the_list = ["a", 2, 3, 1, False, [1, 2, 3]]

for item in the_list[:]:
    if isinstance(item, str):
        del the_list[the_list.index(item)]
    elif isinstance(item, bool):
        del the_list[the_list.index(item)]
    elif isinstance(item, list):
        del the_list[the_list.index(item)]