How do I merge two dictionaries in a single expression in Python?

Python's history and dictionary merging

Back in the time of Python 2.x or Python <3.5, we didn't have these luxurious one-liners. The common way was to resort to loops. Nevertheless, you could maintain simplicity and elegance with this custom function:

def merge_two_dicts(a, b):
    c = a.copy()   # copy 'a' to 'c' as we don't want any royals killed in the battle
    c.update(b)    # updates 'c' with 'b', 'b' wins if powers match
    return c       # return the victorious kingdom

z = merge_two_dicts(x, y)
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This function copies x, containing the battle within and then merges it with y. It's an epic tale of two kingdoms uniting, narrated in Python.

Dealing with deeper issues (Nested dictionaries)

If you are dealing with deeply nested dictionaries, you need to go one level deeper. Adventure awaits with a recursive function:

def deep_merge(d1, d2):
    result = d1.copy()  # Create a copy to avoid effect of the time travel - Bad Wolf!
    for key, value in d2.items():  # Trip starts!
        if isinstance(value, dict) and key in result:
            result[key] = deep_merge(result[key], value)  # We go deeper
        else:
            result[key] = value  # Leveled up reward!
    return result  # BOOM! Mind = Blown
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So, If your dictionaries have hidden chambers (nested dictionaries), this recursive function takes you on a tour to the center of the earth!

Handbook to be a smarter dictionary merger

Always remember safety measures (copy())

It's crucial to think about whether you want to preserve the original dictionaries. Sometimes you may need those originals later, don't give out your secrets so easily!

Your wand need not be heavy (Efficiency matters)

Choosing the most efficient merging technique can give your Python 🐍 superpowers. The speed and memory consumption matter, especially when you're handling dictionary monsters (large ones).

The world isn't just made of strings

Remember, Python dictionaries can use almost any immutable types as keys. So the merging method of dict(x, **y) might leave out some important guests (non-string keys). Be inclusive!

Knowledge is Power (Know your Python version)

Each Python version has its unique charm to merge dictionaries. Learn it, master it and show them who's the boss!