How to make dictionary comprehension in Python

Question

I need advice about comprehensions. Got TypeError: unhashable type: 'list' but I can't see any list coming. (Trying to get dict of indexes and lengths)

data = (
    'abcdefg',
    (10, 20, 30, 40, 50),
    (55,81, 33, 44)
)

# TODO from this:

# lens = dict()
#
# for el in enumerate(data):
#     lens[el[0]] = len(el[1])

# TODO to this
lens = {[el[0]]: len(el[1]) for el in enumerate(data)}

print(lens)

What is the expected output? I think you want `el[0]` instead of `[el[0]]`. `[el[0]]` creates a list — Dani Mesejo, Jul 31 '22 at 09:34
You can unpack the iterator that `enumerate` returns to get a more readable code: `{index: len(li) for index, li in enumerate(data)}` — DeepSpace, Jul 31 '22 at 09:44

Shrirang Mahajan · Accepted Answer · 2022-07-31T09:41:32.697

I suggest this:

data = (
    'abcdefg',
    (10, 20, 30, 40, 50),
    (55,81, 33, 44)
)

# TODO from this:

# lens = dict()
#
# for el in enumerate(data):
#     lens[el[0]] = len(el[1])

# TODO to this
lens = {el[0]: len(el[1]) for el in enumerate(data)}

print(lens)

[el[0]] generates a list. You cannot store list as a key in python dictionaries. Even if list is of only one element. What you need is el[0] as your key.

Output:

{0: 7, 1: 5, 2: 4}

How to make dictionary comprehension in Python

1 Answers1