I want to update one dictionary with another in Python, but if there are some same arguments, their values should be added.
For example:

```
a = {"word_1" : 1, "word_2": 2}
b = {"word_2" : 5, "word_3": 7}

```

Output must be:

```
{"word_1" : 1, "word_2": 7, "word_3": 7}

```

I have googled a lot, but in most answers values rewrites, I want to add them
Here is my solution:

```
    for i in a.keys():
        if i in b.keys():
            b[i] += a[i]
        else:
            b[i] = a[i]

```

Is there most efficient way to do it?