py3.8+中另一种避免big_dict中缺少键的None值的方法使用walrus:

small_dict = {key: val for key in ('l', 'm', 'n') if (val := big_dict.get(key))}

interesting_keys = ('l', 'm', 'n')
subdict = {x: bigdict[x] for x in interesting_keys if x in bigdict}

比较一下所有提到的方法的速度:

更新于2020.07.13(谢谢@user3780389): 仅用于bigdict中的键。

 IPython 5.5.0 -- An enhanced Interactive Python.
Python 2.7.18 (default, Aug  8 2019, 00:00:00) 
[GCC 7.3.1 20180303 (Red Hat 7.3.1-5)] on linux2
import numpy.random as nprnd
  ...: keys = nprnd.randint(100000, size=10000)
  ...: bigdict = dict([(_, nprnd.rand()) for _ in range(100000)])
  ...: 
  ...: %timeit {key:bigdict[key] for key in keys}
  ...: %timeit dict((key, bigdict[key]) for key in keys)
  ...: %timeit dict(map(lambda k: (k, bigdict[k]), keys))
  ...: %timeit {key:bigdict[key] for key in set(keys) & set(bigdict.keys())}
  ...: %timeit dict(filter(lambda i:i[0] in keys, bigdict.items()))
  ...: %timeit {key:value for key, value in bigdict.items() if key in keys}
100 loops, best of 3: 2.36 ms per loop
100 loops, best of 3: 2.87 ms per loop
100 loops, best of 3: 3.65 ms per loop
100 loops, best of 3: 7.14 ms per loop
1 loop, best of 3: 577 ms per loop
1 loop, best of 3: 563 ms per loop

正如预期的那样:字典推导式是最好的选择。

可能:

subdict=dict([(x,bigdict[x]) for x in ['l', 'm', 'n']])

Python 3甚至支持以下内容:

subdict={a:bigdict[a] for a in ['l','m','n']}

注意你可以在字典中检查是否存在，如下所示:

subdict=dict([(x,bigdict[x]) for x in ['l', 'm', 'n'] if x in bigdict])

分别地。对于python 3

subdict={a:bigdict[a] for a in ['l','m','n'] if a in bigdict}

如果有人想要字典的前几项n而不知道键:

n = 5 # First Five Items
ks = [*dikt.keys()][:n]
less_dikt = {i: dikt[i] for i in ks}

至少要短一点:

wanted_keys = ['l', 'm', 'n'] # The keys you want
dict((k, bigdict[k]) for k in wanted_keys if k in bigdict)