input: Write a function to filter book titles containing the word 'Python'.
  assert filter_python_books(['Learning Python', 'Python Cookbook', 'The C++ Programming Language', 'Automate the Boring Stuff with Python']) == ['Learning Python', 'Python Cookbook', 'Automate the Boring Stuff with Python']
  assert filter_python_books(['JavaScript: The Good Parts', 'Effective Java', 'Python Crash Course']) == ['Python Crash Course']
  assert filter_python_books(['C# in Depth', 'Python for Data Analysis', 'Python Tricks']) == ['Python for Data Analysis', 'Python Tricks']
output: def filter_python_books(titles):
      return [title for title in titles if 'Python' in title]