Copy part of dictionary (both its keys and its value)

Question

In my case, I need to transfer part of a dictionary to a persistent storage:

adict={'a':'aaa','b':'bbb','c':'ccc'}
newdict={'a':'aaa','b':'bbb'}

I tried to use dict.fromkeys(['a','b']), this only give me default None Values, unless I specific the value for these keys. What I hope is there is some function automatically default values to the ones the original dict already has. Something like

newdict=adict.fromkeysautomatic(['a','b'])

I know it is easy to write a function to so do so, but I believe there should be some built-in mechanism already, since this should be some frequent behavior. But didn't get it by searching myself.

Answer 1

Using dict comprehension:

>>> d = {'a':'aaa','b':'bbb','c':'ccc'}
>>> newdict = {key:d[key] for key in ['a', 'b']}
>>> newdict
{'a': 'aaa', 'b': 'bbb'}

Side note: Don't use dict as a variable name. It shadows builtin dict function.

Answer 2

Avoiding the dict comprehension which is only available in newer version of Python (2.7+) you can also do:

d = {'a':'aaa','b':'bbb','c':'ccc'}
dd = dict((k, d[k]) for k in ("a", "b"))