How do I create a unique value for each key using dict.fromkeys?

Question

First, I\'m new to Python, so I apologize if I\'ve overlooked something, but I would like to use dict.fromkeys (or something similar) to create a dictionary of

Answer 1

You can also do this if you don't want to learn anything new (although I recommend you do!) I'm curious as to which method is faster?

results = dict.fromkeys(inputs)

for run in range(0, runs):
    for i in inputs:
        if not results[i]:
            results[i] = []
        results[i].append(benchmark(i))

Answer 2

The problem is that in

results = dict.fromkeys(inputs, [])

[] is evaluated only once, right there.

I'd rewrite this code like that:

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))

Other option is:

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))

Answer 3

Check out defaultdict (requires Python 2.5 or greater).

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))