A column encodes "missing" inconsistently — as -999, the empty string '', and the strings 'NA' and 'null' — mixed in with real values. -999 can arrive as an int, a float (-999.0) or the string '-999'; all three are sentinels. Everything else — including 0 — is a real value. Replace every sentinel with None, and report how many you replaced.
Given values: list, return (cleaned, count) where cleaned has None in place of each sentinel.
What the tests check
3 on Run · 4 on Submit01replaces each sentinel encoding with None and counts them
02-999 as a float or a string is a sentinel too
03real values that happen to be falsy are kept
Submit runs these and one more check you don’t see, so code written for the visible tests alone can still miss.