input: Write a function to improve the given function `sum_array` by using Python built-in functions. The original function takes in an array of numbers and returns the sum of all the numbers by manually iterating through the array and adding each element to a total. The improved function should achieve the same result more concisely.
  
  ### Input:
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      total = 0
      for num in array:
          total = total + num
      return total
  
  ### Output:
  def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)
  
  ### Assertions:
  assert sum_array([1, 2, 3, 4, 5])==15
  assert sum_array([10, 20, 30])==60
  assert sum_array([-1, -2, -3, -4, -5])==-15
  assert sum_array([])==0
output: def sum_array(array):
      '''A function that takes in an array of numbers and returns the sum of all the numbers'''
      return sum(array)