Exercise 4: Fix the Crashes — Possible Solution
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colours = ["red", "green", "blue"]
ids = [101, 102, 103]

# print(colours.join(", "))
#   AttributeError: a list has no join method. join belongs to the
#   separator string, not to the list.
print(", ".join(colours))

# print(", ".join(ids))
#   TypeError: join only accepts strings and these are ints.
print(", ".join(map(str, ids)))   # fix 1: convert, then join
print(*ids, sep=", ")             # fix 2: no join, print converts

Output:
red, green, blue
101, 102, 103
101, 102, 103

WHY THIS WORKS AS AN ANSWER
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The first line is a JavaScript habit: arrays have a join method but
Python lists do not, because in Python join lives on the separator
string, so the error is AttributeError. The second is TypeError
because join refuses anything that is not already a string, where
JavaScript would convert silently. Converting first with map(str,
...) keeps join, while print(*ids, sep=', ') avoids join entirely
because print() converts for you.