如何使用dict.fromkeys为每个键创建唯一值？

Question

首先,我是Python的新手,所以如果我忽略了某些内容,我会道歉,但我想使用dict.fromkeys(或类似的东西)来创建列表字典,其中的键在另一个列表中提供.我正在执行一些计时测试,我希望键是输入变量,列表包含运行的时间:

def benchmark(input):
    ...
    return time_taken

runs = 10
inputs = (1, 2, 3, 5, 8, 13, 21, 34, 55)
results = dict.fromkeys(inputs, [])

for run in range(0, runs):
    for i in inputs:
        results[i].append(benchmark(i))

我遇到的问题是字典中的所有键似乎共享相同的列表,每次运行只是附加到它.有没有办法为每个密钥生成一个唯一的空列表fromkeys？如果没有,是否有其他方法可以手动生成结果字典？

Answer 1

查看defaultdict(需要Python 2.5或更高版本).

from collections import defaultdict

def benchmark(input):
    ...
    return time_taken

runs = 10
inputs = (1, 2, 3, 5, 8, 13, 21, 34, 55)
results = defaultdict(list) # Creates a dict where the default value for any key is an empty list

for run in range(0, runs):
    for i in inputs:
        results[i].append(benchmark(i))

Answer 2

问题在于

results = dict.fromkeys(inputs, [])

[]只评估一次,就在那里.

我会像这样重写这段代码:

runs = 10
inputs = (1, 2, 3, 5, 8, 13, 21, 34, 55)
results = {}

for run in range(runs):
    for i in inputs:
        results.setdefault(i,[]).append(benchmark(i))

其他选择是:

runs = 10
inputs = (1, 2, 3, 5, 8, 13, 21, 34, 55)
results = dict([(i,[]) for i in inputs])

for run in range(runs):
    for i in inputs:
        results[i].append(benchmark(i))