input: Write a function to print a histogram based on a list of integers.
  assert print_histogram([4, 9, 7])==None # Expected output: "####", "#########", "#######"
  assert print_histogram([1, 2, 3, 4])==None # Expected output: "#", "##", "###", "####"
  assert print_histogram([0, 5, 2])==None # Expected output: "", "#####", "##"
output: def print_histogram(int_list):
      for num in int_list:
          print('#' * num)