I have a list that looks something like this:

data = ['1', '12', '123']

I want to produce a new list, that looks like this:

result = ['$1', '1', '$2', '12', '$3', '123']

where the number after the $ sign is the length of the next element.

The straightforward way to do this is with a for loop:

result = []
for element in data:
    result += [f'${len(element)}'] + [element]

but I was wondering if it’s possible to do it in a more elegant way – with a list comprehension, perhaps?

I could do

result = [[f'${len(e)}', e] for e in data]

but this results in a list of lists:

[['$1', '1'], ['$2', '12'], ['$3', '123']]

I could flatten that with something like

result = sum([[f'${len(e)}', e] for e in data], [])

or even

result = [x for xs in [[f'${len(e)}', e] for e in data] for x in xs]

but this is getting rather difficult to read. Is there a better way to do this?