Hi there,
I have occasionally gotten division-by-zero errors from this plugin; I
finally decided to look into what's going on. I am having trouble
understanding this code from long_short.py:
Good to know. These seem like valid edge cases you ran into, even if rare,
that the code doesn't handle. I whipped up this plugin for a temporary
need, but have used it permanently since then, and surprisingly haven't run
into these cases (yet).
# ensure our replacement postings sum up to the original
capital gains postings we removed
diff = orig_sum - (short_gains + long_gains)
# divide this diff among short/long. TODO: warn if this is over
tolerance threshold, because it
# means that the transaction is probably not accounted for
correctly
if abs(diff) >= entry.meta['__tolerances__'][p.units.currency]:
total = short_gains + long_gains
short_gains += (short_gains/total) * diff
long_gains += (long_gains/total) * diff
A couple specific questions:
- How could the replacement postings not add up to the original posting?
Rounding errors from various sources.
- If they do, do we really want to be robust to this case, or should that
"TODO" really be TODO: make this a fatal error?
I believe a fatal error beyond a certain threshold is a good idea. Whether
the threshold is the same as the tolerance, some multiple of it, or a fixed
amount is something I meant to figure out but haven't yet. Typically,
brokerages (mine at least) do annoying things like maintain 4 digits of
precision internally but expose only two rounded digits in their ofx/csv,
and thing of that nature. This leads to several cents that I automatically
book to a "Rounding-Error" account in my importers. This I find, works very
well in practice. A rounding error of this nature is typically well above
the transaction's tolerance, and will need to be handled gracefully by this
long_short plugin.
Assuming that there are good reasons to enter this block of code to divvy
up unaccounted for gains/losses, the following seem like problems:
- If short_gains and long_gains are both zero, this code will fail with
div-by-zero.
- If short_gains and long_gains are equal and opposite, this code will also
fail.
Agree, rare but valid edge cases. PR welcome if you get around to fixing it
:).
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