您可以让search函数返回该值。

def search(search_word):
    file = open(path)
    strings = file.read()
    if(search_word in strings):
        return 1
    else:
        return 0

word = input("Enter one word: ")
exists = search(word)

if exists == 1:
    print("This word exists in database!")

else:
    print("This word doesn't exist in database!")

因为你又在函数作用域中定义了exists。
试试这个：

path = 'D:\Python\database.txt'

def search(search_word):
    file = open(path)
    strings = file.read()
    if(search_word in strings):
        exists = 1
    else:
        exists = 0
    return exists

还有

word = input("Enter one word: ")
    exists = search(word)

    if exists == 1:
        print("This word exists in database!")

    else:
        print("This word doesn't exist in database!")

现在你的函数只是将变量exists设置为1或0。exists是一个 * 局部变量 。根据定义，你应该不*从其他地方访问它。如果你想知道这个值，你需要添加return。

path = 'D:\Python\database.txt'

def search(search_word):
    file = open(path)
    strings = file.read()
    if(search_word in strings):
        return 1
    else:
        return 0

在添加return之后，你需要在某个地方接收值。你可以按照其他注解中的建议去做，并将它保存到变量exists中，或者你可以按照我下面的建议去做。因为你将使用结果作为if-else来检查return是0还是1，所以你可以立即检查if (search(word)):以获得一个更干净的代码。

def main():
    word = input("Enter one word: ")

    if search(word):
        print("This word exists in database!")
    else:
        print("This word doesn't exist in database!")

if __name__ == "__main__":
    main()