Python Quiz n1 — Merging Python dictionaries

Every week we publish a Python quiz in my twitter account. Only for fun!

The summary of question for this weed was:

• Subject: Dictionaries
• Difficulty: 2/5

You can reach the question at the original tweet:

Correct answer

Ok. Spoiler here. Correct answer is Option C. But, why…?

A brief explanation

Before all, the question assumes we’re using Python 3. Python 2 was dead, oks?

Why Option A is incorrect

It looks like:

a = {“one”: “two”}
b = {“nine”: “ten”}
merged = a | b

Ok. This choice was a bit tricky. Syntax a | b is new in Python 3.9. So, this answer is correct.

You can find more info at official Python documentation:

What's New In Python 3.9 - Python 3.9.0 documentation

So: this option is true. Then is not a valid answer

Option B

It looks like:

a = {“one”: “two”}
b = {“nine”: “ten”}
merged = {**a, **b}

In Python 3.5 was introduced this syntax. So this options is also true (or True? :D)

So: this option is true. Then is not a valid answer

Option C

It looks like:

a = {“one”: “two”}
b = {“nine”: “ten”}
merged = a + b

Operator add (+) is not implemented for Python dictionaries. So, if you try to do that you’ll get an error like:

>>> a = {“one”: “two”}
>>> b = {“nine”: “ten”}
>>> a + b
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'dict' and 'dict'

So: this option is false. Then is the correct answer

Extra: Making Option C true

As I said, operator add is not implemented for dictionaries in Python by default. But you can overload it. It’s ver easy:

class dictp(dict):

    def __add__(self, o: dict):
        tmp = self.copy()
        tmp.update(o)
        return tmp

Now you must use dictp instead of regular dict:

>>> a = dictp()
>>> a["one"] = 1
>>> b = dictp()
>>> b["two"] = 2
>>> print(a + b)
{'one': 1, 'two': 2}

Any question or suggestion? Leave me a comment!