How to create a dictionary from a list of keys and a dictionary of values in Python?

Question

I have a dictionary of key: value pairs and a list of keys as below:

dict1 = {'a':(1, 2), 'b':(2,2), 'c':(3,3), 'd':(4,4)}
list1 = ['a', 'c']

I now want to create a new dictionary that only contains the key:value pairs taken from list1. So the end result is list2 below:

list2 = {'a':(1, 2), 'c':(3,3)}

Help would be much appreciated. I'm currently using python 2.5.4 if that makes any difference?

Thank you in advance. Tom

Answer 1

one nice expression, even in 2.5 you have a simple solution

dict((k, dict1[k]) for k in list1)

dict has an initializer that takes an iterable of tuples. The inner expression produces one tuple at a time, looking over the keys in list1 and getting the values from dict1

The above will result in a KeyError if list1 contains a key not in dict1 , if that's the case then the below will work by looking at the keys in the dict and checking for its presence in list1

dict((k, v) for k, v in dict1.iteritems() if k in list1)

Answer 2

You could do this:

dict2 = {}
for key in list1:
    dict2[key] = dict1[key]

(I renamed list2 to dict2 , it seemed to make more sense).

Answer 3

Something like this :

new_dict = {}
for i in list1:
    new_dict[i] = dict1[i]

Answer 4

You can do this with a simple loop:

result = {}

for item in list1:
    result[item] = dict1[item]

Or, in 2.7+, with a dict comprehension:

result = {key: value
          for key, value in dict1.items()
              if key in list1}

Answer 5

Just do something simple like:

for item in list1:
    list2[item] = dict1[item]