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Negative zero not preserved #3144
Description
Zarr version
v3.0.8
Numcodecs version
v0.15.1
Python Version
3.11
Operating System
Mac
Installation
pip in a venv
Description
Negative zero (-0.0) is not distinguished from zero when reading back values from a Zarr array. This differs from the expected behaviour (and Zarr Python v2).
Steps to reproduce
# /// script
# requires-python = ">=3.11"
# dependencies = [
# "zarr@git+https://github.com/zarr-developers/zarr-python.git@main",
# ]
# ///
#
# This script automatically imports the development branch of zarr to check for issues
import numpy as np
import zarr
print(zarr.array(np.array([0.0, -0.0]))[:])
#zarr.print_debug_info()This prints
[0. 0.]
But with Zarr 2.18.7 it correctly prints
[ 0. -0.]
Additional output
No response
Activity
d-v-b commentedon Jun 18, 2025
thanks for this report, I did a quick check and this bug was present prior to the recent dtype changes, so that should help narrow the search down a bit.
tomwhite commentedon Jun 18, 2025
Yes, sorry I forgot to say it is in 3.0.8 as well as main.
d-v-b commentedon Jun 18, 2025
Adding a non-0 fill value preserves the signed 0 as expected. I also checked that the original test case doesn't write any chunks. So the error comes from zarr mistakenly identifying the chunk as empty during array creation, thenfailing to write it, which results in zarr using the fill value instead on indexing.
tomwhite commentedon Jun 18, 2025
Aha - which explains why it works on v2 - the default for
write_empty_chunksis True (it's False in v3). On v2 the following fails too:d-v-b commentedon Jun 18, 2025
I suspect we are relying on this behavior:
We probably need to define a stricter type of equality.
Write chunks with negative zero values and a zero fill value
Write chunks with negative zero values and a zero fill value
Write chunks with negative zero values and a zero fill value
Write chunks with negative zero values and a zero fill value
Write chunks with negative zero values and a zero fill value (#3216)
perf: cut the fill_value check on the chunk write path
perf: cut the fill_value check on the chunk write path (#4382)