Python Dictionary with List as Keys and Tuple as Values

Question

I have a list that I want to use as the keys to a dictionary and a list of tuples with the values. Consider the following:

d = {}
l = ['a', 'b', 'c', 'd', 'e']
t = [(1, 2, 3, 4), (7, 8, 9, 10), (4, 5, 6, 7), (9, 6, 3, 8), (7, 4, 1, 2)]

for i in range(len(l)):
    d[l[i]] = t[i]

The list will consistently be 5 values and there will consistently be 5 tuples however there are hundreds of thousands of values in each tuple.

My question is this: what is the FASTEST way to populate the dictionary, d, with the tuples in t, with the keys being the values in l?

Sven Marnach · Accepted Answer · 2011-05-31 16:52:53Z

17

I did no timings, but probably

d = dict(zip(l, t))

will be quite good. For only 5 key-value pairs, I don't think izip() will provide any advantage over zip(). The fact that each tuple has a lot of items does not matter for this operation, since the tuple objects are not copied at any point, neither with your approach nor with mine. Only pointers to the tuple objects are inserted in the dicitonary.

answered May 31, 2011 at 16:52

Sven Marnach

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Community · Accepted Answer · 2017-05-23 11:48:44Z

9

To build on Sven's answer, using itertools.izip would be faster and use less memory if you needed to create a larger dict. With only five key/value pairs the time to build the dict will be miniscule.

python -m timeit -s "l = l2 = range(100000)" "dict(zip(l, l2))" 
1000 loops, best of 3: 20.1 msec per loop
python -m timeit -s "import itertools; l = l2 = range(100000)" "dict(itertools.izip(l, l2))"
1000 loops, best of 3: 9.59 msec per loop

edited May 23, 2017 at 11:48

CommunityBot

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answered May 31, 2011 at 17:08

Zach Kelling

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2 Comments

Sven Marnach Over a year ago

These timings use a lot more than 5 key-value pairs, so I'm not surprised about the difference. For only 5 key-value pairs, the difference will be immaterial. (BTW, +1 for actually measuring instead of guessing!)

Zach Kelling Over a year ago

@Sven That's a good point. With only 5 key-value pairs, speed will be minuscule either way.

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