input: Write a function to calculate the sum of a list of numbers. The function should take a list of numbers as input and return the sum of the elements in the list.
  
  def sum_list(arr):
      """Calculates the sum of a given list of numbers.
      
      Args:
          arr (list): List of numbers.
          
      Returns:
          int: Sum of list elements.
      """
      sum = 0
      for num in arr:
          sum += num
      return sum
  
  assert sum_list([1, 2, 3, 4, 5]) == 15
  assert sum_list([-1, -2, -3, -4, -5]) == -15
  assert sum_list([]) == 0
  assert sum_list([10, 20, 30, 40, 50]) == 150
  assert sum_list([0, 0, 0, 0, 0]) == 0
output: def sum_list(arr):
      sum = 0
      for num in arr:
          sum += num
      return sum