Constructing a new dict:

dict_you_want = {key: old_dict[key] for key in your_keys}

Uses dictionary comprehension.

If you use a version which lacks them (ie Python 2.6 and earlier), make it dict((key, old_dict[key]) for ...). It's the same, though uglier.

Note that this, unlike jnnnnn's version, has stable performance (depends only on number of your_keys) for old_dicts of any size. Both in terms of speed and memory. Since this is a generator expression, it processes one item at a time, and it doesn't looks through all items of old_dict.

Removing everything in-place:

unwanted = set(old_dict) - set(your_keys)
for unwanted_key in unwanted: del your_dict[unwanted_key]

How about this:

In Python 3.x :

def slicedict(d, s):
    return {k:v for k,v in d.items() if k.startswith(s)}

in Python 2.x :

def slicedict(d, s):
    return {k:v for k,v in d.iteritems() if k.startswith(s)}

How about a dict comprehension:

filtered_dict = {k: v for k, v in d.iteritems() if filter_string in k}

One you see it, it should be self-explanatory, as it reads like English pretty well.

This syntax requires Python 2.7 or greater.

In Python 3, there is only dict.items(), not iteritems() so you would use:

filtered_dict = {k: v for k, v in d.items() if filter_string in k}

You can't do such directly with dict[keyword]. You have to iterate through the dict and match each key against the keyword and return the corresponding value if the keyword is found. This is going to be an O(N) operation.

>>> my_dict = {'name': 'Klauss', 'age': 26, 'Date of birth': '15th july'}
>>> next(v for k,v in my_dict.items() if 'Date' in k)
'15th july'

To get all such values use a list comprehension:

>>> [ v for k, v in my_dict.items() if 'Date' in k]
['15th july']

use str.startswith if you want only those values whose keys starts with 'Date':

>>> next( v for k, v in my_dict.items() if k.startswith('Date'))
'15th july'
>>> [ v for k, v in my_dict.items() if k.startswith('Date')]
['15th july']