Stop setting copy to False by default

[jeanconn]

Description

Don't set default of copy=False in __init__.

In numpy > 2 the copy=False default causes an error if the operation cannot be done without a copy. In numpy < 2.0 this was benign as copy=False was equivalent to "copy if you have to". But changing to not set the default appears to be benign in ska with numpy < 2.0 and the astropy Time default was already to not-copy so a change here appears to be non-impacting.

Interface impacts

Testing

Unit tests

• Mac on ska3-latest (numpy < 2)

(latest) flame:cxotime jean$ git rev-parse HEAD
59d104b70102f4ea55c14969aa65edfcef33b3f2
(latest) flame:cxotime jean$ pytest
============================= test session starts ==============================
platform darwin -- Python 3.12.8, pytest-8.3.4, pluggy-1.5.0
rootdir: /Users/jean/git
configfile: pytest.ini
plugins: anyio-4.7.0, timeout-2.3.1
collected 292 items                                                            

cxotime/tests/test_cxotime.py .......................................... [ 14%]
........................................................................ [ 39%]
........................................................................ [ 63%]
........................................................................ [ 88%]
...................                                                                                                                                       [ 94%]
cxotime/tests/test_cxotime_linspace.py ...............                                                                                                    [100%]

====================================================================== 292 passed in 1.63s

Independent check of unit tests by Javier

• OSX:

(ska3-flight-2026.0rc4) ~/SAO/git/cxotime unset-copy-default $ git rev-parse HEAD       
a00bd8e183b26a8783cc350615376a15242b304f
(ska3-flight-2026.0rc4) ~/SAO/git/cxotime unset-copy-default $ pytest cxotime           
==================================================================== test session starts =====================================================================
platform darwin -- Python 3.13.10, pytest-9.0.1, pluggy-1.6.0
rootdir: /Users/javierg/SAO/git
configfile: pytest.ini
plugins: anyio-4.12.0, timeout-2.4.0
collected 292 items                                                                                                                                          

cxotime/tests/test_cxotime.py ........................................................................................................................ [ 41%]
...................................................................................................................................................... [ 92%]
.......                                                                                                                                                [ 94%]
cxotime/tests/test_cxotime_linspace.py ...............                                                                                                 [100%]

==================================================================== 292 passed in 1.52s =====================================================================
(ska3-flight-2026.0rc4) ~/SAO/git/cxotime unset-copy-default $ conda deactivate                    
(ska3-flight) ~/SAO/git/cxotime unset-copy-default $ pytest cxotime  
==================================================================== test session starts =====================================================================
platform darwin -- Python 3.12.8, pytest-8.3.4, pluggy-1.5.0
rootdir: /Users/javierg/SAO/git
configfile: pytest.ini
plugins: anyio-4.7.0, timeout-2.3.1
collected 292 items                                                                                                                                          

cxotime/tests/test_cxotime.py ........................................................................................................................ [ 41%]
...................................................................................................................................................... [ 92%]
.......                                                                                                                                                [ 94%]
cxotime/tests/test_cxotime_linspace.py ...............                                                                                                 [100%]

==================================================================== 292 passed in 1.60s =====================================================================

Functional tests

No functional testing.

[jeanconn]

@taldcroft @javierggt should we configure this to be backward compatible using numpy version testing?

[javierggt]

Tests pass with this version on flight. What happens on flight if the default is not set?

[javierggt]

What Tom was suggesting yesterday was to use astropy.utils.compat.NUMPY_LT_2_0 (I checked that it is defined on flight, so it is not a problem to do it.

[jeanconn]

Right, Tom was suggesting "astropy.utils.compat.NUMPY_LT_2_0" for use in a different package, but we could use it here. I don't know if it is strictly required that we preserve the copy False behavior for numpy < 2.0 because it wasn't clear to me if numpy was actually managing to do the operation without a copy. But maybe it is lowest impact to just do the if statement.

[javierggt]

I am guessing that Tom put that statement there because otherwise it would be copied. This is a performance thing.

Unfortunately, no test fails on flight when I remove the line, so I would have to think which case that was intended for.

[javierggt]

I have tried a few things to get a test to fail in flight when I remove that statement, and no luck. I don't know what corner case this is meant for.

[taldcroft]

To be honest I do not recall why I put that there. The upstream default (in astropy Time) is already to not copy, so I believe this is currently a no-op in flight. Things might have been different when I wrote CxoTime.

In any case, we should not clutter the code with this conditional since tests are currently passing in flight.

[taldcroft]

For the record: https://docs.astropy.org/en/stable/api/astropy.time.Time.html#astropy.time.Time.