Maintaining type through a transformation

[RickBradford]

Please excuse a basic question from a functional-first programmer, but I am trying to work out how to maintain the type (or class) of a list after I transform it.

So, I have a class called Story, and I create several instances of that in a list.

(setv storys (readwords "stories.txt"))

I now update that list using a 'map' function and place it in a new variable.

(setv updatedstorys (list (map(fn [s] (updater.update s)) storys)))

If I check the variable 'updatedstorys', the list has the correct number of elements, but the compiler does not recognize that the list contains Story elements, and produces an error.

(lfor s updatedstorys (print (s.name + " " + endtime.strftime ("%d-%B" ) + " - " + s.perc) ))

AttributeError: 'NoneType' object has no attribute 'name'

Any pointers on how to do this correctly would be much appreciated.

[allison-casey]

Without knowing the surrounding code, my best guess is that updater.update is returning None

[RickBradford]

Yes, that's what it was - a failure in my understanding of Python rather than Hy.

While I'm trying to sort out this bit of code, could I ask what the correct Hy syntax would be for the Python datetime code:

datetimeobj=datetime.datetime.strptime(s.date,"%Y-%m-%d")
endtime = datetimeobj + datetime.timedelta(days=s.gap)
print (endtime.strftime("%d %B"))

Thanks for your help

[scauligi]

Translating directly to Hy, it'll look like this:

(setv datetimeobj (datetime.datetime.strptime s.date "%Y-%m-%d")
      endtime (+ datetimeobj (datetime.timedelta :days s.gap)))
(print (endtime.strftime "%d %B"))

[RickBradford]

Many thanks.

What a fine project this is - I recently needed to learn Python after a long time working almost exclusively in F#, and find it to be a very useful but rather dull language. Hy is a much more interesting take on Python.