Even i'm facing the same issue. My code looked like this:
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total = 0
for item in food:
total += item
And this returned error "Oops, try again. compute_bill(['apple']) resulted in a TypeError: unsupported operand type(s) for +=: 'int' and 'str'"
This is because i thought he argument 'food' is a list. But it turned out to be a dictionary.
So, modifying the last second line to "total += prices[item]" solved my issue.
My question is: where did we mention that 'food' is a dictionary and not a list????