What is the easiest and most direct way to create a dictionary comprehension in Python 3?

General Discussions
1

I found the following post on of the community about python dictionary comprehension in Python 2.7 and Python 3+, stating that I can apply dictionary comprehensions like this:

d = {key: value for (key, value) in sequence}

I tried it in Python 3, but it raises an exception.

d = {'a':1, 'b':2, 'c':3, 'd':4}
{key : value for (key, value) in d}
{key : value for key, value in d}

Both versions raise a ValueError saying: ValueError: need more than 1 value to unpack.

What is the easiest and most direct way to create a dictionary comprehension in Python 3?

2

In Python 3, when you try to loop over a dictionary directly, it iterates over the keys. To unpack both the key and value, you need to explicitly use .items().

d = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
result = {key: value for key, value in d.items()}  # python dictionary comprehension.

This is the easiest and most direct way to create a dictionary comprehension where you access both the keys and values.

3

If you want to filter or transform the dictionary entries in the comprehension, you can add a condition. Here’s an example that filters out any keys that are not in the alphabet range ‘a’ to ‘c’:

d = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
result = {key: value for key, value in d.items() if key in ['a', 'b', 'c']}  # python dictionary comprehension.

This version demonstrates how you can apply conditions to create a filtered version of your dictionary using python dictionary comprehension.

4

You can also use python dictionary comprehension to apply a transformation to the keys or values. For example, multiplying the values by 2:

d = {'a': 1, 'b': 2, 'c': 3, 'd': 4}
result = {key: value * 2 for key, value in d.items()}  # python dictionary comprehension

This solution shows how to use dictionary comprehension to modify the values while iterating through the dictionary.