Question

Updating a Dictionary

When working with lists, you probably noticed that you can change the value at a given index with a simple assignment statement. So, for example, the following code replaces the first element of lst with 42:

    lst[0] = 42

You can update the value for a given key in a dictionary in the same way. The general syntax for this is:

    d[key] = value

This is also how you insert new key/value pairs to a dictionary; if the key does not exist, it will be added.

Write a function add_to_dict(d, key_value_pairs) which adds each given key/value pair to the given dictionary. The argument key_value_pairs will be a list of tuples in the form (key, value).

The function should return a list of all of the key/value pairs which have changed (with their original values).

Answer 1

def add_to_dict(d, key_value_pairs):
    res = dict()
    for x in key_value_pairs:
        if(not x[0] in d.keys()):
            d[x[0]] = x[1]
        else:
            res[x[0]] = d[x[0]]
            d[x[0]] = x[1]
    return res