astropy: SystemError: returned NULL without setting an error

I’m sorry @bsipocz for some reason I never got a notification of your comment. Disabling fast_writer=False makes the issue go away.

I can reproduce this bug with Python 3.7 and Astropy 3.0.4 .

Minimal test case to reproduce:

$ conda create --name trouble python=3.7 astropy
$ conda activate trouble
$ python
Python 3.7.0 | packaged by conda-forge | (default, Aug  7 2018, 14:28:25) 
[Clang 6.1.0 (clang-602.0.53)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import astropy
>>> astropy.__version__
'3.0.4'
>>> from astropy.table import Table
>>> t = Table({'a': [1, 2, 3]})
>>> t.write('test.csv')
>>> t.write('test.csv')
WARNING: AstropyDeprecationWarning: test.csv already exists. Automatically overwriting ASCII files is deprecated. Use the argument 'overwrite=True' in the future. [astropy.io.ascii.ui]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/deil/software/anaconda3/envs/gammapy-dev-37/lib/python3.7/site-packages/astropy/table/table.py", line 2562, in write
    io_registry.write(self, *args, **kwargs)
  File "/Users/deil/software/anaconda3/envs/gammapy-dev-37/lib/python3.7/site-packages/astropy/io/registry.py", line 560, in write
    writer(data, *args, **kwargs)
  File "/Users/deil/software/anaconda3/envs/gammapy-dev-37/lib/python3.7/site-packages/astropy/io/ascii/connect.py", line 86, in write_csv
    return write(table, filename, **kwargs)
  File "/Users/deil/software/anaconda3/envs/gammapy-dev-37/lib/python3.7/site-packages/astropy/io/ascii/ui.py", line 881, in write
    writer.write(table, output)
  File "/Users/deil/software/anaconda3/envs/gammapy-dev-37/lib/python3.7/site-packages/astropy/io/ascii/fastbasic.py", line 194, in write
    self._write(table, output, {'fill_values': [(core.masked, '')]})
  File "/Users/deil/software/anaconda3/envs/gammapy-dev-37/lib/python3.7/site-packages/astropy/io/ascii/fastbasic.py", line 170, in _write
    writer = cparser.FastWriter(table, **write_kwargs)
SystemError: <class 'astropy.io.ascii.cparser.FastWriter'> returned NULL without setting an error

Note how the error is only triggered on the second write call.

I also tried with Astropy master (e9dee2e9589adfe4f0c803246add11164da03b83) and the issue seems to be resolved; so possibly just making a new Astropy release would resolve it.

But maybe it’s worth adding a regression test for this?

Note that if you try to run Astropy tests with Python 3.7 you might run into this pytest bug at the moment: https://github.com/pytest-dev/pytest/issues/3854#issuecomment-415671196

@taldcroft or anyone - thoughts?

Thanks for checking!

It does not.

$ conda list
# packages in environment at /home/gabriel/anaconda3/envs/asteca3:
#
# Name                    Version                   Build  Channel
astropy                   3.0.4            py37h14c3975_0  
atomicwrites              1.1.5                    py37_0  
attrs                     18.1.0                   py37_0  
autograd                  1.2                       <pip>
blas                      1.0                         mkl  
ca-certificates           2018.03.07                    0  
certifi                   2018.8.13                py37_0  
cycler                    0.10.0                   py37_0  
cython                    0.28.5           py37hf484d3e_0  
dbus                      1.13.2               h714fa37_1  
emcee                     2.2.1              pyh24bf2e0_4    astropy
expat                     2.2.5                he0dffb1_0  
fontconfig                2.13.0               h9420a91_0  
freetype                  2.9.1                h8a8886c_0  
future                    0.16.0                    <pip>
glib                      2.56.1               h000015b_0  
gst-plugins-base          1.14.0               hbbd80ab_1  
gstreamer                 1.14.0               hb453b48_1  
icu                       58.2                 h9c2bf20_1  
intel-openmp              2018.0.3                      0  
jpeg                      9b                   h024ee3a_2  
kiwisolver                1.0.1            py37hf484d3e_0  
libedit                   3.1.20170329         h6b74fdf_2  
libffi                    3.2.1                hd88cf55_4  
libgcc-ng                 7.2.0                hdf63c60_3  
libgfortran-ng            7.2.0                hdf63c60_3  
libpng                    1.6.34               hb9fc6fc_0  
libstdcxx-ng              7.2.0                hdf63c60_3  
libuuid                   1.0.3                h1bed415_2  
libxcb                    1.13                 h1bed415_1  
libxml2                   2.9.8                h26e45fe_1  
matplotlib                2.2.2            py37hb69df0a_2  
mkl                       2018.0.3                      1  
mkl_fft                   1.0.4            py37h4414c95_1  
mkl_random                1.0.1            py37h4414c95_1  
more-itertools            4.2.0                    py37_0  
ncurses                   6.1                  hf484d3e_0  
numpy                     1.15.0           py37h1b885b7_0  
numpy-base                1.15.0           py37h3dfced4_0  
openssl                   1.0.2p               h14c3975_0  
pandas                    0.23.3           py37h04863e7_0  
patsy                     0.5.0                    py37_0  
pcre                      8.42                 h439df22_0  
pip                       10.0.1                   py37_0  
pip                       18.0                      <pip>
pluggy                    0.6.0                    py37_0  
psutil                    5.4.6            py37h14c3975_0  
py                        1.5.4                    py37_0  
pyparsing                 2.2.0                    py37_1  
pyqt                      5.9.2            py37h22d08a2_0  
pytest                    3.6.3                    py37_0  
pytest-arraydiff          0.2              py37h39e3cac_0  
pytest-astropy            0.4.0                    py37_0  
pytest-doctestplus        0.1.3                    py37_0  
pytest-openfiles          0.3.0                    py37_0  
pytest-remotedata         0.3.0                    py37_0  
python                    3.7.0                hc3d631a_0  
python-dateutil           2.7.3                    py37_0  
pytz                      2018.5                   py37_0  
qt                        5.9.6                h52aff34_0  
readline                  7.0                  ha6073c6_4  
sampyl-mcmc               0.3                       <pip>
scipy                     1.1.0            py37hc49cb51_0  
seaborn                   0.9.0                    py37_0  
setuptools                39.2.0                   py37_0  
sip                       4.19.8           py37hf484d3e_0  
six                       1.11.0                   py37_1  
sqlite                    3.24.0               h84994c4_0  
statsmodels               0.9.0            py37h035aef0_0  
tk                        8.6.7                hc745277_3  
tornado                   5.0.2            py37h14c3975_0  
wheel                     0.31.1                   py37_0  
xz                        5.2.4                h14c3975_4  
zlib                      1.2.11               ha838bed_2