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Quantity created with copy=True doesn't owndata #7244
Description
It seems that the copy keyword for creating Quantity doesn't do what I expect it to, namely ensuring that the returned Quantity actually owns the data:
>>> import numpy
>>> from astropy.units import Quantity
>>> a = numpy.arange(4)
>>> print(a.flags.owndata)
True
>>> b = Quantity(a)
>>> print(b.flags.owndata)
False
>>> c = Quantity(a, copy=True)
>>> print(c.flags.owndata)
False
>>> d = Quantity(a).copy()
>>> print(d.flags.owndata)
TrueThis is all because internal to Quantity.__new__ the .value property is set using ndarray.view.
If the copy keyword is supposed to guarantee data ownership, can Quantity.__new__ get modified to use Quantity.copy, otherwise can the documentation be expanded a wee bit to highlight this potential confusion?
Maybe I've just missed some documentation that already exists somewhere, if so, sorry for the spam.
Activity
Array: use .copy() to ensure data ownership
mhvk commentedon Feb 28, 2018
@duncanmmacleod - I think a
Quantitycan, as currently written, never own its data as it is always constructed via a view of anndarray(which itself, though, holds a new copy of the data). In principle, I guess this could be changed by doing something likeand then copying the data to self.
Since we're doing the copy anyway, maybe there is a way to do this more immediately -- worth investigating since it might also speed up initialization just a little bit...
mhvk commentedon Feb 28, 2018
p.s. The way I usually test data is a copy is via
np.may_share_memory.