sort() 和 reverse() 函数不起作用

问题描述

我试图根据我正在阅读的教程测试 python 中的列表是如何工作的.当我尝试使用 list.sort() 或 list.reverse() 时，解释器给了我 None.

请告诉我如何从这两种方法中获得结果:

a = [66.25, 333, 333, 1, 1234.5]打印(a.sort())打印(a.reverse())

解决方案

.sort() 和 .reverse() 更改列表就地 并返回 None 参见 mutable序列文档:

sort() 和 reverse() 方法在排序或反转大列表时修改列表以节省空间.提醒您它们是通过副作用操作的，它们不会返回排序或反转的列表.

改为这样做:

a.sort()打印(一)a.反向()打印(一)

或使用 sorted() 和 reversed() 函数.

print(sorted(a)) # 刚刚排序print(list(reversed(a))) # 刚刚反转print(a[::-1]) # 使用负切片步骤反转print(sorted(a, reverse=True)) # sorted *and* reversed

这些方法返回一个新列表并保持原始输入列表不变.

演示，就地排序和反转:

>>>a = [66.25, 333, 333, 1, 1234.5]>>>a.sort()>>>打印(一)[1, 66.25, 333, 333, 1234.5]>>>a.反向()>>>打印(一)[1234.5, 333, 333, 66.25, 1]

并创建新的排序和反向列表:

>>>a = [66.25, 333, 333, 1, 1234.5]>>>打印(排序(一))[1, 66.25, 333, 333, 1234.5]>>>打印(列表(反转(a)))[1234.5, 1, 333, 333, 66.25]>>>打印(a[::-1])[1234.5, 1, 333, 333, 66.25]>>>打印(排序(一个，反向=真))[1234.5, 333, 333, 66.25, 1]>>>a # 输入列表未受影响[66.25, 333, 333, 1, 1234.5]

I was trying to test how the lists in python works according to a tutorial I was reading.When I tried to use list.sort() or list.reverse(), the interpreter gives me None.

Please let me know how I can get a result from these two methods:

a = [66.25, 333, 333, 1, 1234.5]
print(a.sort())
print(a.reverse())

解决方案

.sort() and .reverse() change the list in place and return None See the mutable sequence documentation:

Do this instead:

a.sort()
print(a)
a.reverse()
print(a)

or use the sorted() and reversed() functions.

print(sorted(a))               # just sorted
print(list(reversed(a)))       # just reversed
print(a[::-1])                 # reversing by using a negative slice step
print(sorted(a, reverse=True)) # sorted *and* reversed

These methods return a new list and leave the original input list untouched.

Demo, in-place sorting and reversing:

>>> a = [66.25, 333, 333, 1, 1234.5]
>>> a.sort()
>>> print(a)
[1, 66.25, 333, 333, 1234.5]
>>> a.reverse()
>>> print(a)
[1234.5, 333, 333, 66.25, 1]

And creating new sorted and reversed lists:

>>> a = [66.25, 333, 333, 1, 1234.5]
>>> print(sorted(a))
[1, 66.25, 333, 333, 1234.5]
>>> print(list(reversed(a)))
[1234.5, 1, 333, 333, 66.25]
>>> print(a[::-1])
[1234.5, 1, 333, 333, 66.25]
>>> print(sorted(a, reverse=True))
[1234.5, 333, 333, 66.25, 1]
>>> a  # input list is untouched
[66.25, 333, 333, 1, 1234.5]

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