sorted(a,key = cmp_to_key(cmp))
时间: 2024-05-26 22:12:18 浏览: 16
这是一行 Python 代码,它使用了 cmp_to_key 函数和 key 参数来对列表 a 进行排序。具体来说,cmp_to_key 函数用于将旧的比较函数转换为新的“键函数”,而 key 参数则指定用于排序的“键函数”。在这个例子中,cmp 是一个旧的比较函数,它将被转换为一个键函数,并用于对列表 a 进行排序。需要注意的是,Python 3 中已经删除了 cmp 函数,所以这段代码不能在 Python 3 中使用。
相关问题
key=functools.cmp_to_key
The `functools.cmp_to_key` function is a utility function in Python's `functools` module that helps convert a comparison function to a key function.
In Python, sorting a list of objects requires a way to compare the objects. This is done by providing a comparison function that takes two objects as input and returns `-1`, `0`, or `1` depending on whether the first object is less than, equal to, or greater than the second object.
However, some sorting functions in Python (such as the `sorted` function) require a key function instead of a comparison function. A key function takes a single object as input and returns a value that can be used for sorting.
The `cmp_to_key` function helps convert a comparison function to a key function by returning a new function that takes a single object as input and returns a tuple `(comparison_result, object)` where `comparison_result` is the result of calling the original comparison function with the input object and another object, and `object` is the input object itself. This tuple can then be used for sorting.
Here's an example of how to use `cmp_to_key`:
```
from functools import cmp_to_key
def compare_length(str1, str2):
if len(str1) < len(str2):
return -1
elif len(str1) > len(str2):
return 1
else:
return 0
strings = ['cat', 'dog', 'elephant', 'a', 'zebra']
sorted_strings = sorted(strings, key=cmp_to_key(compare_length))
print(sorted_strings)
# Output: ['a', 'cat', 'dog', 'zebra', 'elephant']
```
In this example, we define a comparison function `compare_length` that compares the lengths of two strings. We then use `cmp_to_key` to convert this comparison function to a key function, and pass it to the `sorted` function to sort a list of strings by length. The resulting sorted list is `['a', 'cat', 'dog', 'zebra', 'elephant']`.
for item in sorted(dic.items(), key=functools.cmp_to_key(compare)): if len(item[1]) > 0: res.append(str(item[0])) print(','.join(res))
这段代码的作用是按照指定的比较函数 `compare` 对字典 `dic` 进行排序,然后将排序后的字典项中,值非空的键转换成字符串,并用逗号连接起来打印输出。
其中,`sorted()` 函数用于对字典 `dic` 进行排序,排序的结果是一个元组列表,每个元组由键和值组成。`key` 参数指定排序时所采用的比较函数,`functools.cmp_to_key()` 函数将比较函数转换为一个键函数,用于在排序过程中进行比较。在每个元组中,`item[0]` 表示键,`item[1]` 表示值。`len(item[1]) > 0` 用于判断值是否非空,如果非空就将键转换为字符串并添加到 `res` 列表中。最后,使用 `','.join(res)` 将 `res` 列表中的字符串用逗号连接起来,并打印输出。
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