Question

我是python的新手，正在从事一个小项目：

90、75、65、50、40是以下等级

我的代码：

grade1 = int(input("Enter grade 1:"))
grade2 = int(input("Enter grade 2:"))
grade3 = int(input("Enter grade 3:"))
grade4 = int(input("Enter grade 4:"))
grade5 = int(input("Enter grade 5:"))

numbers = [grade1,grade2,grade3,grade4,grade5]
sorted_grades = sorted(numbers)
topthree = sorted_grades[-1,-2,-3]

但是，在运行topthree时我收到一个错误：

TypeError：列表索引必须是整数或切片，而不是元组

如何避免这种情况？

Answer 1

您需要像这样使用列表切片：

topthree = sorted_grades[:-4:-1]

我知道它说-4，但它排在前三位。

如果要使用列表，则需要花费更多的精力：

indices = [-1, -2, -3]
topthree = [sorted_grades[i] for i in indices]

您还可以反向排序：

sorted_grades = sorted(numbers, reverse=True)
topthree = sorted_grades[:3]

Answer 2

假设您已经将成绩收集到名为grades的列表中：

# New list of sorted entries
sorted_grades = sorted(grades)

# Sum of all list entries divided by the length
average = sum(grades)/len(grades)
# Last entry minus the first entry
range = grades[-1] - grades[0]
# Slice from the third-to-last entry to the end of the list
top_three = grades[-3:]

tutorial provided in the CPython documentation中进一步讨论了诸如负索引和切片之类的语法：

像字符串（和所有其他内置序列类型）一样，可以对列表进行索引和切片：
>>> squares = [1, 4, 9, 16, 25]
>>> squares
[1, 4, 9, 16, 25]
>>> squares[0]  # indexing returns the item
1
>>> squares[-1]
25
>>> squares[-3:]  # slicing returns a new list
[9, 16, 25]
所有切片操作都返回一个包含所请求元素的新列表。这意味着以下切片将返回列表的新（浅）副本：
>>> squares[:]
[1, 4, 9, 16, 25]

列表索引/切片的一般格式为some_list[start:stop:step]：

>>> numbers = [1,3,5,7,9]
>>> numbers[0:3]  # slice from the first element to the third
[1, 3, 5]
>>> numbers[:3]  # 0's can be omitted
[1, 3, 5]
>>> numbers[1:3]  # slice from the second element to the third
[3, 5]
>>> numbers[3:]  # slice from the third element to the end
[7, 9]
>>> numbers[-3:]  # slice from the third-to-last to the end
[5, 7, 9]
>>> numbers[::-1]  # slice of the whole list, stepping backward by 1 for each entry
[9, 7, 5, 3, 1]
>>> numbers[1::2]  # slice of every other entry, starting with the second
[3, 7]

请注意，列表切片是不包含结尾的，因此numbers[1:2]仅返回第二个条目：[3]。

Answer 3

Python使用:符号进行列表切片。因此，不要使用topthree = sorted_grades[-1,-2,-3]，而要使用topthree = sorted_grades[-1:-4:-1]。列表切片的格式为[start:stop:step]。

如何在没有TypeError的情况下从此列表中找到范围，平均值和前三个值？

3 个答案: