Python sum() function with list parameter

Have you used the variable sum anywhere else? That would explain it.

>>> sum = 1
>>> numbers = [1, 2, 3]
>>> numsum = (sum(numbers))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not callable

The name sum doesn't point to the function anymore now, it points to an integer.

Solution: Don't call your variable sum, call it total or something similar.

numbers = [1, 2, 3]
numsum = sum(list(numbers))
print(numsum)

This would work, if your are trying to Sum up a list.