input: Write a function that improves the given function by using Python built-in functions. The original function takes in an array of numbers and returns the sum of all the numbers by iterating through each number in the array and adding it to a total variable. The improved function should simplify this process using a Python built-in function.
  
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)
  
  assert sum_array([1, 2, 3, 4, 5])==15
  assert sum_array([10, 20, 30])==60
  assert sum_array([-1, 0, 1])==0
  assert sum_array([])==0
  assert sum_array([-5, 5, -5, 5])==0
output: def sum_array(array):
      return sum(array)