3-7 缩减名单：你刚得知新购买的餐桌无法及时送达，因此只能邀请两位嘉宾。
- 以完成练习3-6时编写的程序为基础，在程序末尾添加一行代码，打印一条你只能邀请两位嘉宾共进晚餐的消息。
- 使用pop() 不断地删除名单中的嘉宾，直到只有两位嘉宾为止。每次从名单中弹出一位嘉宾时，都打印一条消息，让该嘉宾知悉你很抱歉，无法邀请他来共进晚餐。
- 对于余下的两位嘉宾中的每一位，都打印一条消息，指出他依然在受邀人之列。
- 使用del 将最后两位嘉宾从名单中删除，让名单变成空的。 打印该名单，核实程序结束时名单确实是空的。
Solution：
friends = ["Tim", "Tom", "Pat", "Coco"]
for friend in friends:
print("I would like to have dinner with you, " + friend + '.')
print("\nI have found a larger table to have dinner.")
friends.insert(0, "Ashero")
friends.insert(2, "Lily")
friends.append("Faker")
for friend in friends:
print("I would like to have dinner with you, " + friend + '.')
print("\nMy new table counldn't arrive in time. I can only invite 2 people.")
print("Sorry, " + friends.pop() + ". I counldn't invite you to my dinner!")
print("Sorry, " + friends.pop() + ". I counldn't invite you to my dinner!")
print("Sorry, " + friends.pop() + ". I counldn't invite you to my dinner!")
print("Sorry, " + friends.pop() + ". I counldn't invite you to my dinner!")
print("Sorry, " + friends.pop() + ". I counldn't invite you to my dinner!\n")
for friend in friends:
print("You still can have dinner with me, " + friend + '.')
del friends[0]
del friends[0]
print(friends)Output：
I would like to have dinner with you, Tim.
I would like to have dinner with you, Tom.
I would like to have dinner with you, Pat.
I would like to have dinner with you, Coco.
I have found a larger table to have dinner.
I would like to have dinner with you, Ashero.
I would like to have dinner with you, Tim.
I would like to have dinner with you, Lily.
I would like to have dinner with you, Tom.
I would like to have dinner with you, Pat.
I would like to have dinner with you, Coco.
I would like to have dinner with you, Faker.
My new table counldn't arrive in time. I can only invite 2 people.
Sorry, Faker. I counldn't invite you to my dinner!
Sorry, Coco. I counldn't invite you to my dinner!
Sorry, Pat. I counldn't invite you to my dinner!
Sorry, Tom. I counldn't invite you to my dinner!
Sorry, Lily. I counldn't invite you to my dinner!
You still can have dinner with me, Ashero.
You still can have dinner with me, Tim.
[]注：学习了循环之后应该可以将代码pop()的部分简化。
3-8 放眼世界：想出至少5个你渴望去旅游的地方。
- 将这些地方存储在一个列表中，并确保其中的元素不是按字母顺序排列的。
- 按原始排列顺序打印该列表。不要考虑输出是否整洁的问题，只管打印原始Python列表。
- 使用sorted() 按字母顺序打印这个列表，同时不要修改它。
- 再次打印该列表，核实排列顺序未变。
- 使用sorted() 按与字母顺序相反的顺序打印这个列表，同时不要修改它。
- 再次打印该列表， 核实排列顺序未变。
- 使用reverse()修改列表元素的排列顺序。打印该列表，核实排列顺序确实变了。
- 使用reverse() 再次修改列表元素的排列顺序。打印该列表，核实已恢复到原来的排列顺序。
- 使用sort() 修改该列表，使其元素按字母顺序排列。打印该列表，核实排列顺序确实变了。
- 使用sort() 修改该列表，使其元素按与字母顺序相反的顺序排列。打印该列表，核实排列顺序确实变了。
Solution：
places = ["Japan", "America", "England", "Canada", "Australia"]
print(places)
print(sorted(places))
print(places)
print(sorted(places, reverse = True))
print(places)
places.reverse()
print(places)
places.reverse()
print(places)
places.sort()
print(places)
places.sort(reverse = True)
print(places)Output：
['Japan', 'America', 'England', 'Canada', 'Australia']
['America', 'Australia', 'Canada', 'England', 'Japan']
['Japan', 'America', 'England', 'Canada', 'Australia']
['Japan', 'England', 'Canada', 'Australia', 'America']
['Japan', 'America', 'England', 'Canada', 'Australia']
['Australia', 'Canada', 'England', 'America', 'Japan']
['Japan', 'America', 'England', 'Canada', 'Australia']
['America', 'Australia', 'Canada', 'England', 'Japan']
['Japan', 'England', 'Canada', 'Australia', 'America']3-9 晚餐嘉宾：在完成练习3-4~练习3-7时编写的程序之一中，使用len() 打印一条消息，指出你邀请了多少位嘉宾来与你共进晚餐。
Solution：
friends = ["Tim", "Tom", "Pat", "Coco"]
for friend in friends:
print("I would like to have dinner with you, " + friend + '.')
print("I have invited " + str(len(friends)) + " people to my dinner.")Output：
I would like to have dinner with you, Tim.
I would like to have dinner with you, Tom.
I would like to have dinner with you, Pat.
I would like to have dinner with you, Coco.
I have invited 4 people to my dinner.注：len(列表)的输出是一个数字，需要用强制类型转换str()才能和字符串一起操作。