如何将列表值与字典键进行比较并使用 python 创建一个新字典

Question

I have a list like this:

lis = ['Date', 'Product', 'Price']

I want to compare it with:

dict = {'Date' : '2013-05-01', 'Salary' : '$5000', 'Product' : 'Toys', 'Price' : '$10', 'Salesman' : 'Smith'}

I want to compare each item of list with keys of dictionary and make a new dictionary.
What I have tried is:

n = {}
for k,v in dict.items():
    for i in lis:
        if i==k:
            n[k] = v

Output:

n = {'Date' : '2013-05-01', 'Product' : 'Toys', 'Price' : '$10'}

This works but I want to do it through generators - can someone help me do that?

Answer 1

Treat lis as a set instead, so you can use dictionary views and an intersection:

# python 2.7:
n = {k: d[k] for k in d.viewkeys() & set(lis)}

# python 3:
n = {k: d[k] for k in d.keys() & set(lis)}

Or you could use a simple dict comprehension with a in test against d :

# python 2.6 or older:
n = dict((k, d[k]) for k in lis if k in d)

# python 2.7 and up:
n = {k: d[k] for k in lis if k in d}

This presumes that not all values in lis are going to be in d ; the if k in d test can be dropped if they are always going to be present.

For your specific case, the second form is quite a lot faster:

>>> from timeit import timeit
>>> timeit("{k: d[k] for k in d.viewkeys() & s}", 'from __main__ import d, lis; s=set(lis)')
2.156520128250122
>>> timeit("{k: d[k] for k in lis if k in d}", 'from __main__ import d, lis')
0.9401540756225586

Answer 2

filtered_dict = dict((k, original_dict[k]) for k in lis if k in original_dict)

Or if you have 2.7+:

filtered_dict = {k: original_dict[k] for k in lis if k in original_dict}

If you want to use a generator:

item_generator = ((k, original_dict[k]) for k in lis if k in original_dict)

The generator will yield (key, value) pairs.

Answer 3

For Python 3.6

dict_keys_list = list(dict.keys())
dict_keys_list.sort()
for key in dict_keys_list:
     if key in lis:
          print("Key is present")

Another approach where you want to compare a list of keys to be equal to the dictionary keys.

person = { 'name' : 'Don', 'nickname' : 'John', 'age' : 45, 'salary' : 50000, 'place' : 'Monaco, Europe' }
compare_list = ['nickname', 'place', 'name', 'salary', 'age']
person_keys_list = list(person.keys())
person_keys_list.sort()
compare_list.sort()
person_keys_list == compare_list # Gives you True