Ludium - Learn by Doing

Keep Only the Positives, In Place

Assume you are given a list L whose elements are numbers. Write a function keep_positives(L) that mutates L in place so that only the strictly positive numbers remain, in their original order.

The function returns nothing, and the caller must see the change through the very same list object it passed in — do not rebind L to a newly built list.

nums = [3, -1, 0, 7, -8]
keep_positives(nums)
nums   ->  [3, 7]

def keep_positives(L):
    """Mutate the list L in place so that only the strictly positive numbers
    it contains remain, in their original order. Returns None."""
    pass

def keep_positives(L):
    """Mutate the list L in place so that only the strictly positive numbers
    it contains remain, in their original order. Returns None."""
    pass

Scratchpad— run any Python to test ideas

# Scratchpad — run any Python here to test ideas.
# Anything you write below stays separate from the problem's tests.

print("hello, world")

# Scratchpad — run any Python here to test ideas.
# Anything you write below stays separate from the problem's tests.

print("hello, world")

Python runtime ready in a moment

Visible tests · 2Examples — click to expand

[3, -1, 0, 7, -8] becomes [3, 7]

the function returns None (it mutates instead)

Hidden tests · 3Bodies hidden — pass/fail only

Hidden test 1

Hidden test 2

Hidden test 3

Coding challenges on cloning, removing, and copying lists

Keep Only the Positives, In Place

Coding challenges on cloning, removing, and copying lists

Keep Only the Positives, In Place