CODEWITHSUNDEEP
pythonperformanceloopsdictionarycopy
Tim
Tim

Reputation: 7464

Copy multiple items between dictionaries

I want to copy selected elements between dictionaries. Is there a better/more efficient way than this:

dict1 = {'a' : 1, 'b' : 2, 'c' : 3, 'd' : 4}
list = ['a', 'd']

dict2 = { k : dict1[k] for k in dict1 if k in list }

?

Upvotes: 0

Views: 312

Answers (3)

John La Rooy
John La Rooy

Reputation: 304255

There's the functional way

>>> dict1 = {'a' : 1, 'b' : 2, 'c' : 3, 'd' : 4}
>>> lst = ['a', 'd']
>>> dict(zip(lst, map(dict1.get, lst)))
{'a': 1, 'd': 4}

or

>>> from operator import itemgetter
>>> dict(zip(lst, itemgetter(*lst)(dict1)))
{'a': 1, 'd': 4}

But they are ~3 times slower than the dict comprehension :)

Upvotes: 1

TerryA
TerryA

Reputation: 59984

Yes, use dict.get() and iterate through the list of keys instead of the dictionary.

>>> {k:dict1.get(k) for k in list1}
{'a': 1, 'd': 4}

Note, you shouldn't override the built-in type list.

This is especially helpful as if k isn't a key in dict1, then None is returned.

Upvotes: 4

Lennart Regebro
Lennart Regebro

Reputation: 172279

Yes there is:

 dict2 = { k : dict1[k] for k in list }

Upvotes: 4

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