Is there a way to get the previous partition_key from context in an asset?

hi @Nicholas Pezolano -- if you're using a time-based partitions definition (e.g. DailyPartitionsDefinition) then you can do something like

@asset(partitions_def=my_partitions)
def my_asset(context):
    current_partition_window = context.partition_time_window
    previous_partition_window = my_partitions.get_prev_partition_window(current_partition_window)

this will give you a TimeWindow object which will have start and end datetime properties indicating the time range of that partition window. If you want to turn that into a partition key, you can do

my_partitions.get_partition_key_range_for_time_window(previous_partition_window).start

previous_partition_window = edi_partitions_def.get_prev_partition_window(current_partition_window)
  File "C:\Users\n\anaconda3\lib\site-packages\dagster\_core\definitions\time_window_partitions.py", line 346, in get_prev_partition_window
    prev_window = next(windows_iter)
  File "C:\Users\n\anaconda3\lib\site-packages\dagster\_core\definitions\time_window_partitions.py", line 576, in _reverse_iterate_time_windows
    end_timestamp = pendulum.instance(end, tz=self.timezone).timestamp()
  File "C:\Users\n\anaconda3\lib\site-packages\pendulum\__init__.py", line 174, in instance
    raise ValueError("instance() only accepts datetime objects.")

I got the above error when I tried that,

current_partition_window

is indeed returning a

TimeWindow

object

TimeWindow(start=DateTime(2023, 2, 14, 18, 15, 0, tzinfo=Timezone('America/New_York')), end=DateTime(2023, 2, 15, 18, 15, 0, tzinfo=Timezone('America/New_York')))

ah that's pretty odd -- what version of

pendulum

are you on? this should theoretically work regardless of version but just want to narrow down the possibilities

I'm on 2.1.2 with pendulum, is it because I'm formatting my partition?

DailyPartitionsDefinition(start_date="2023-01-12",  
                          fmt='%Y-%m-%d',
                          timezone='America/New_York', 
                          minute_offset=30,
                          hour_offset=16)

ah my bad, I had a typo in the original code -- it should be

previous_partition_window = my_partitions.get_prev_partition_window(current_partition_window.start)

Thanks