Repository navigation
Tables with 2D columns of strings fail round trip to FITS format under py3 #5287
Description
Example using astropy 1.2.1 and python 3.5:
In [1]: #- Tables with 1D columns of strings can round-trip to FITS just fine, including
...: #- the encoding/decoding to get form unicode to bytes and back
...: t1 = Table()
...: t1['x'] = ['aa', 'bb', 'cc']
...: t1.write('t1.fits', overwrite=True)
...: t2 = Table.read('t1.fits')
...: t1.dtype, t2.dtype
...:
Out[1]: (dtype([('x', '<U2')]), dtype([('x', '<U2')]))
In [2]: t1['x'] == t2['x']
...:
Out[2]: array([ True, True, True], dtype=bool)
In [3]: #- Add a 2D column of strings and try again:
...: t2['y'] = [['x', 'xx'], ['y', 'yy'], ['z', 'zz']]
...: t2.write('t2.fits', overwrite=True)
...: t3 = Table.read('t2.fits')
...: t2.dtype, t3.dtype
...:
Out[3]:
(dtype([('x', '<U2'), ('y', '<U2', (2,))]),
dtype([('x', '<U2'), ('y', '<U8', (2,))]))Note that the dtype for 'y' column has changed from '<U2' to '<U8'.
This works for python 2.7, where the dtype remains 'S2'.
Note that this problem is covered by the unit tests reported in #5280, but the discussion there has focused on the underlying io.fits library and how to create a BinTableHDU, so I'm separating this out as a separate Table-focused issue since that isolates the user from the underlying I/O library.
Activity