Repository navigation
QTable converts numbers to float, if unit is unknown #15447
Description
Description
When loading a fits file with a numeric column in which is formatted as an int with an associated unit that QTable does not recognize, the column is changed to a float.
Expected behavior
Report a warning about the unit, but do not change the dtype of the data (this is what happens when I read with Table).
How to Reproduce
>>> from astropy.table import Table, QTable
>>> t = Table({'a':[1,2,3], 'b': [4., 5., 6.]})
>>> t['a'].unit = 'channel'
>>> t.write('test.fits', format='fits', overwrite=True)
WARNING: UnitsWarning: 'channel' did not parse as fits unit: At col 0, Unit 'channel' not supported by the FITS standard. If this is meant to be a custom unit, define it with 'u.def_unit'. To have it recognized inside a file reader or other code, enable it with 'u.add_enabled_units'. For details, see https://docs.astropy.org/en/latest/units/combining_and_defining.html [astropy.units.core]
>>> tab = Table.read('test.fits')
>>> tab
<Table length=3>
a b
channel
int64 float64
------- -------
1 4.0
2 5.0
3 6.0
>>> tab = QTable.read('test.fits')
>>> tab
<QTable length=3>
a b
channel
float64 float64
------- -------
1.0 4.0
2.0 5.0
3.0 6.0Versions
macOS-13.2.1-arm64-arm-64bit
Python 3.9.9 | packaged by conda-forge | (main, Dec 20 2021, 02:41:07)
[Clang 11.1.0 ]
astropy 6.0.dev776+g40e6ed90d2
Numpy 1.22.0
pyerfa 2.0.0.1
Scipy 1.7.3
Matplotlib 3.5.1
Activity
pllim commentedon Oct 5, 2023
Whether the unit is valid or not doesn't matter. Quantity always cast the values to float. I get the same behavior even if I set the unit to meters.
I think this behavior was reported elsewhere (even when QTable is not involved) but I cannot find the issue now, maybe @mhvk remembers.
mhvk commentedon Oct 12, 2023
There is tentative PR for fixing this at #12505. Note that there was quite a bit of discussion of exactly when one should upcast, but I think it was most of the way there...
taldcroft commentedon Sep 23, 2026
Fixed by #20273.