Functions with "search in a book" example.

playpen2.py

import random

def query(book):
    query_string = input("What do you want to look for?")

    if query_string in book:
        print("Yes, it is in the book.")
    else:
        print("No, it is not in the book")


def main():
    book = ["This", "is", "my", "greatest","book","ever"]
    book2 = ["This", "is", "my", "worst","book","ever"]
    query(book)
    query(book2)


main()

Just a little suggestion, adding \n to the end of the string in the input function makes it so that the user types one line below the question. Example:

query_string = input("What do you want to look for?\n")