Compare two dictionaries, remove key/value pair in one dict if it exists in the other

Question

I have two dictionaries. One looks like this:

dict1 = {'ana': 'http://ted.com', 'louise': 'http://reddit.com', 'sarah':'http://time.com'}

The other one looks like this:

dict2 = {'patricia': 'http://yahoo.com', 'ana': 'http://ted.com',
         'louise': 'http://reddit.com', 'florence': 'http://white.com'}

I need to compare the two dictionaries, and eliminate from dict2 any key/value pair already present in dict1

As you can see, Ana and Louise already exist in dict1 , so I'd like to automatically delete it from dict2 The output expected would contain only elements unique to dict2 and not already present in dict1 , and would look like:

dict2 = {'patricia': 'http://yahoo.com', 'florence': 'http://white.com'}

I don't need to do anything about Sarah being in dict1 . I only care about comparing dict2 with dict1 to remove duplicates.

Extra info:

I tried to loop over the dicts in many different ways but it gave me two types of errors: not hashable type or dict content changed during action .

I also tried to make each into a list and combine the lists, but the end result is another list and I don't know how to turn a list back into a dictionary.

Answer 1

Jim's answer removes items if the keys match. I think you wanted to remove if both key and value matched. This is actually very easy since you're using Python 3:

>>> dict(dict2.items() - dict1.items())
{'florence': 'http://white.com', 'patricia': 'http://yahoo.com'}

It works because dict_items objects treat subtraction operations as set differences.

Answer 2

如果你们中的任何人正在寻找python 2.x的解决方案（因为我一直在寻找），那么这就是答案：

dict(filter(lambda x: x not in dict2.items(), dict1.items()))

Answer 3

Then just use a dictionary comprehension:

dict2 = {i:j for i,j in dict2.items() if i not in dict1}

which results in dict2 being:

{'florence': 'http://white.com', 'patricia': 'http://yahoo.com'}

An in-place solution could be:

for k in dict1:
    dict2.pop(k, None)

which yields a similar result.

Answer 4

This simply looks for all the keys in dict1 that are in dict2 and then deletes the key/value pairs from dict2.

for key in dict1:
    if key in dict2 and (dict1[key] == dict2[key]):
        del dict2[key]

Hoe this helps!