universal copy-and-modify function by nstarman · Pull Request #15750 · astropy/astropy

nstarman · 2023-12-15T17:18:27Z

TODO:

tests
changelog & what's new
documentation
implement this in a whole bunch more places

As came up in discussion in #15643, it would be very convenient to have a consistent means to copy an instance, replacing a certain set of attributes. In Cosmology there's clone, in BaseCoordinateFrame there's replicate.
This PR doesn't replace these methods (which should still be made consistent), rather introducing a new universal framework styled off of the dataclasses function replace. With replace any Astropy object can easily register an implementation for copy-and-modify!

>>> from astropy.utils import replace
>>> replace(skycoord, new_attr=...)
>>> replace(quantity, unit=...)
...

How does this work? functools.singledispatch means one function (replace) is defined in the module astropy.utils.replace. Normally you would need a big if-else list to handle different data types. Or roll a custom registration system. functools.singledispatch takes care of the registration for us and is well documented in core python, so this is an easy system to teach and is a very stable solution. All you need to do register support for a new type is

from astropy.utils import replace

@replace.register
def _register_mytype(obj: MyType, /, **kwargs: Any) -> MyType:
    ...

functools.singledispatch introspects the function for the annotations and handles everything. replace.register can also accept arguments directly. See functools for details.

P.S. functools.singledispatch also handles subclasses very well.
P.P.S. I registered dataclasses.replace into astropy.utils.replace, so ALL dataclasses are supported!

Long-term note:
If this PR is adopted I actually think we should plan to spin it off into a micro-package that becomes a runtime dependency for Astropy. It's such a simple (and IMO elegant) solution to the copy-and-modify issue that I think this will be genuinely useful far outside of Astropy, at the very least in coordinated and affiliate packages. Since it's just a simple wrapper around a core-python future, this will be a very stable dependency. But we can discuss this plan after this PR.

By checking this box, the PR author has requested that maintainers do NOT use the "Squash and Merge" button. Maintainers should respect this when possible; however, the final decision is at the discretion of the maintainer that merges the PR.

github-actions · 2023-12-15T17:18:56Z

github-actions · 2023-12-15T17:19:01Z

👋 Thank you for your draft pull request! Do you know that you can use [ci skip] or [skip ci] in your commit messages to skip running continuous integration tests until you are ready?

nstarman · 2023-12-15T17:20:36Z

+
+
+@replace.register
+def _replace_quantity(obj: _QuantityT, /, **kwargs: Any) -> _QuantityT:


This handles Quantity subclasses, but we might want some more specific functions that better address nuances.

Styled off of the dataclasses function. Signed-off-by: nstarman <[email protected]>

nstarman · 2023-12-15T17:33:39Z

Ping @ayshih (as a note, you're not in the any-can-join public Astropy Members group so I can't request a review)

nstarman · 2023-12-15T17:37:06Z

+    unit = kwargs.pop("unit", obj.unit)
+    return type(obj)(value, unit=unit, **kwargs)


Suggested change

unit = kwargs.pop("unit", obj.unit)

return type(obj)(value, unit=unit, **kwargs)

kwargs.setdefault("unit", obj.unit)

return type(obj)(value, **kwargs)

pllim · 2023-12-15T20:42:19Z

Re: group membership -- The automation that Matt Craig set up a while ago is currently broken. But I have manually invited ayshih to astropy-contributors group. Hopefully he accepts!

ayshih · 2023-12-18T15:12:11Z

Re this PR: It's an interesting approach! I think the challenge would be to educate users that this function even exists, since I imagine that the natural inclination would continue to be to hunt for the appropriate class-specific method. It doesn't help that astropy.utils is currently more for developers than for non-developer users, so I don't know if the latter group would even think to look there.

Re adding me to astropy-contributors: Thanks! (I was curious, so I looked up when I first contributed to Astropy, and it was in September 2015.)

nstarman · 2023-12-18T15:45:54Z

I think the challenge would be to educate users that this function even exists, since I imagine that the natural inclination would continue to be to hunt for the appropriate class-specific method.

The docs would be the most natural place, I suppose. Most classes in Astropy don't have a class-specific method, so hunting will only turn up replace :)

It doesn't help that astropy.utils is currently more for developers than for non-developer users, so I don't know if the latter group would even think to look there.

Agreed. This is a larger problem we have. We need to better distinguish utils for users, utils for affiliate package developers, and internal utils.

mhvk

I left a few in-line comments, but like @ayshih, I worry about visibility for these kinds of small "handy" functions. Indeed, it may not see that much use even in astropy (less than 10 true uses of .replicate, mostly in SpectralCoordinate and Time). Given those cases, I think there will be very little outside use (as far as I can tell from a quick check, I do not ever use .replicate myself). It seems to me it really mostly makes sense in a modeling situation (this including Cosmology), where it is meaningful to just replace one attribute.

Overall, maybe just try to make cosmology and modeling have a consistent interface?

mhvk · 2023-12-18T18:22:50Z

+    """
+    # Currently ``replicate`` is not implemented for SkyCoord and returns a
+    # ``BaseCoordinateFrame``object.
+    return obj.__class__(obj.replicate(copy=copy, **kwargs))


Realize this is still a draft just to see whether we want it at all, but this won't be quite right, since all non-frame attributes get lost.

mhvk · 2023-12-18T18:24:59Z

@@ -0,0 +1,46 @@
+"""
+A simple class to manage a piece of global science state.  See


copy & paste error?

nstarman · 2024-04-16T21:42:24Z

I guess this would be better handled as an external library. It's a generically useful solution to a common Python problem.

github-actions Bot added units coordinates visualization labels Dec 15, 2023

nstarman commented Dec 15, 2023

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nstarman force-pushed the universal-replace branch from 24caa2e to 1c873ab Compare December 15, 2023 17:28

universal replace function

6292069

Styled off of the dataclasses function. Signed-off-by: nstarman <[email protected]>

nstarman force-pushed the universal-replace branch from 1c873ab to 6292069 Compare December 15, 2023 17:29

nstarman added the whatsnew-needed label Dec 15, 2023

nstarman changed the title ~~universal replace function~~ universal copy-and-modify function Dec 15, 2023

nstarman commented Dec 15, 2023

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pllim removed the visualization label Dec 15, 2023

pllim added this to the v6.1.0 milestone Dec 15, 2023

pllim requested a review from ayshih December 18, 2023 15:19

mhvk reviewed Dec 18, 2023

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nstarman mentioned this pull request Jan 14, 2024

Change Integrator.run to call GalacticDynamics/galax#50

Merged

astrofrog modified the milestones: v6.1.0, v7.0.0 Apr 4, 2024

nstarman closed this Apr 16, 2024

nstarman mentioned this pull request Jun 19, 2024

Provide a way to make a copy of a model with different parameter values, or be more flexible with parameter shape #16593

Closed

nstarman mentioned this pull request Dec 9, 2024

Implement __replace__ method for CPython 3.13 #16887

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universal copy-and-modify function - #15750

universal copy-and-modify function#15750
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		@replace.register
		def _replace_quantity(obj: _QuantityT, /, **kwargs: Any) -> _QuantityT:

		unit = kwargs.pop("unit", obj.unit)
		return type(obj)(value, unit=unit, **kwargs)

		@@ -0,0 +1,46 @@
		"""
		A simple class to manage a piece of global science state. See

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