input: Write a python function to check if a string contains the word "python".
  assert contains_python("I love programming in python.") == True
  assert contains_python("This is a Python script.") == False
  assert contains_python("Learning python is fun.") == True
  assert contains_python("Python is a popular programming language.") == True
  assert contains_python("I am writing code in Java.") == False
output: def contains_python(s):
      return "python" in s.split()