Rather than try and detect if you are at the last item, print the comma and newline when printing the next (which only requires detecting if you are at the first):
a = ['hello', 9, 3.14, 9]
for i, item in enumerate(a):
if i: # print a separator if this isn't the first element
print(',')
print(item, end='')
print() # last newline
The enumerate() function adds a counter to each element (see What does enumerate mean?), and if i: is true for all values of the counter except 0 (the first element).
Or use print() to insert separators:
print(*a, sep=',\n')
The sep value is inserted between each argument (*a applies all values in a as separate arguments, see What does ** (double star) and * (star) do for parameters?). This is more efficient than using print(',n'.join(map(str, a))) as this doesn't need to build a whole new string object first.
