How can this be written on a single line?

Question

I've seen some Python list comprehensions before, but can this be done in a single line of Python?

errs = {}
for f in form:
    if f.errors:
        errs[f.auto_id] = f.errors

Answer 1

errs = dict((f.auto_id, f.errors) for f in form if f.errors)

Answer 2

It probably could be, but as per the “Readability counts.” rule (PEP 20), I'd say it's a bad idea. :)

On the other hand you have “Flat is better than nested.” and “Sparse is better than dense.”, so I guess it's a matter of taste :)

Answer 3

Python 3.0 has dict comprehensions as a shorter/more readable form of the anser provided by Steef:

errs = {f.auto_id: f.errors for f in form if f.errors}

Answer 4

Both ways are quite readable, however you should think of future maintainers of the code. Sometimes explicit is better. List comprehensions rule though :)