input: Write a python function to count the number of non-empty lines in a file.
  assert count_non_empty_lines("example1.txt") == 10
  assert count_non_empty_lines("example2.txt") == 5
  assert count_non_empty_lines("example3.txt") == 0
output: def count_non_empty_lines(filename):
      with open(filename, 'r') as file:
          return sum(1 for line in file if line.strip())