How to Merge Two Lists of Dictionaries in Python Using ** Unpacking

A student wanted to merge two lists of dictionaries, l1 and l2, into a single list where each element is a dictionary containing the keys from both original dictionaries.

l1 = [{x: x} for x in range(10)]
l2 = [{x: x} for x in range(10, 20)]

The desired result looks like:

[{0: 0, 10: 10}, {1: 1, 11: 11}, {2: 2, 12: 12}, {3: 3, 13: 13}, {4: 4, 14: 14}, {5: 5, 15: 15}, {6: 6, 16: 16}, {7: 7, 17: 17}, {8: 8, 18: 18}, {9: 9, 19: 19}]

Python 3.5+ provides a convenient syntax for merging dictionaries: {**x, **y}. For example, merging two simple dictionaries:

d1 = {"a": 1, "b": 2}
d2 = {"c": 3, "d": 4}
# Resulting dictionary, with later keys overriding earlier ones
d3 = {**d1, **d2}  # {'a': 1, 'b': 2, 'c': 3, 'd': 4}

Using this syntax, we can merge the dictionaries inside l1 and l2 as follows:

l3 = []
for x, y in zip(l1, l2):
    l3.extend([{**x, **y}])
print(l3)

This code zips the two lists, merges each pair of dictionaries with the {**x, **y} unpacking, and extends l3 with the merged dictionaries, producing the desired combined list.