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Bugfix: Array * TimeDelta fails for mysterious reason #1455

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taldcroft merged 1 commit into from
Oct 18, 2013
Merged

Bugfix: Array * TimeDelta fails for mysterious reason #1455

taldcroft merged 1 commit into from
Oct 18, 2013
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@mhvk mhvk commented Oct 14, 2013

Multiplying an nd.array with a TimeDelta fails, as the numpy function tries to get an item that does not exist (independent of whether TimeDelta is an array or not. It seems TimeDelta never gets a chance to try (the reverse -- TimeDelta * Array works fine); somehow, numpy fails to return NotImplemented? Mysterious.

In [1]: from astropy.time import Time, TimeDelta; import numpy as np

In [2]: np.array(1)*TimeDelta(100., format='sec')
ERROR: TypeError: scalar 'TimeDelta' object is not subscriptable. [astropy.time.core]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-91a8a4ea9a5c> in <module>()
----> 1 np.array(1)*TimeDelta(100., format='sec')

/home/mhvk/packages/astropy/astropy/time/core.py in __getitem__(self, item)
    506         if self.isscalar:
    507             raise TypeError('scalar {0!r} object is not subscriptable.'.format(
--> 508                 self.__class__.__name__))
    509         tm = self.replicate()
    510         jd1 = self._time.jd1[item]

TypeError: scalar 'TimeDelta' object is not subscriptable.

@mhvk mhvk mentioned this pull request Sep 15, 2013
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mhvk commented Oct 14, 2013

@taldcroft - the odd behaviour I noticed with array*time was due to Time not being properly prepared to deal with arrays. One needs to set __array_priority__ and also ensure that __len__ fails for scalar values (see a stackoverflow query by @astrofrog [1]). With that introduced,

from astropy.time import Time, TimeDelta; import numpy as np
np.arange(10.)*TimeDelta(100., format='sec')

yields

<TimeDelta object: scale='tai' format='sec' value=[   0.  100.  200.  300.  400.  500.  600.  700.  800.  900.]>

as it should. The one disadvantage is that len(t) for single times now gives a TypeError (but the same is true for arrays, quantities, etc.).

[1] http://stackoverflow.com/questions/7667799/numpy-object-arrays

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mhvk commented Oct 18, 2013

@taldcroft - if you have a chance to review -- this is really quite a small bugfix...

taldcroft added a commit that referenced this pull request Oct 18, 2013
@taldcroft
Merge pull request #1455 from mhvk/time-array-priority
0b0a85f 
Bugfix: Array * TimeDelta fails for mysterious reason
@taldcroft taldcroft merged commit 0b0a85f into astropy:master Oct 18, 2013
@mhvk mhvk deleted the time-array-priority branch October 18, 2013 03:56
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@mhvk @taldcroft