Im confused about this error in python

Question

When i type this

def books_available(books):
    """Show a list of books to buy."""
    for book in books:
    books_in_stock = "the following title is available to buy" + books.title() + "."
    available = ['elon musk', 'The everything store', 'The growth hack']
    books_available(available)
    print(books_available)
    it gives me this

  File "<ipython-input-6-d36a60b7cf5a>", line 4
    books_in_stock = "the following title is available to buy" + books.title() + "."
    ^
IndentationError: expected an indented block

can you help