Nested Sum

In Doc2Doc, users can process files or entire directories. We need to know the total size of those files and directories (measured in bytes).

Due to the nested nature of directories, we represent a root directory as a list of lists. Each list represents a directory, and each number represents the size of a file in that directory. For example, here's a directory that contains 2 files at the root level, then a nested directory with its own two files:

root: list[int | list] = [1, 2, [3, 4]]
print(sum_nested_list(root))
# 10

Here's a more complex example:

root
├── scripts.txt (5 bytes)
├── characters (dir)
│   ├── zuko.txt (6 bytes)
│   └── aang.txt (7 bytes)
└── seasons (dir)
    ├── season1 (dir)
    │   ├── the_avatar_returns.docx (8 bytes)
    │   └── the_southern_air_temple.docx (9 bytes)
    └── season2_notes.txt (10 bytes)

Which would be represented as:

root: list[int | list] = [5, [6, 7], [[8, 9], 10]]
print(sum_nested_list(root))
# 45

Complete the sum_nested_list function. It takes a nested list of integers as input and should return the total size of all files in the list. It's a recursive function.

Here's some pseudocode to help you get started:

1. Create an integer variable to keep track of the total size.
2. For each item in the list (use a loop here):
   1. If the item is an integer, add it to the total size.
   2. If the item is a list, use a recursive call to sum_nested_list to get the size of that list. Add that size to the total size.
3. Return the total size when you're done iterating.

• You can use loops with recursion. While functional programming avoids loops, recursion is also used outside functional programming.
• The built-in isinstance function can tell you if an item is an integer or a list:

  isinstance(5, list)
  # False
  isinstance([5, 6], list)
  # True