np.strings.find raises ValueError for a table MaskedColumn #20257

In [2]: from astropy.table.column import MaskedColumn
   ...: import numpy as np
   ...: 
   ...: 
   ...: data = ["foo", "bar", "baz"]
   ...: col = MaskedColumn(data=data, mask=False, fill_value="N/A", dtype=np.dtype("<U8"))
   ...: np.char.find(col, "foo")
Out[2]: array([ 0, -1, -1])

In [3]: astropy.__version__
Out[3]: '6.1.7'

In [4]: np.__version__
Out[4]: '1.26.4'

from astropy.table.column import MaskedColumn
import numpy as np


data = ["foo", "bar", "baz"]
col = MaskedColumn(data=data, mask=False, fill_value="N/A", dtype=np.dtype("<U8"))
np.strings.find(col, "foo")

In [33]: np.strings.find(col, "foo")
Out[33]: ---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/numpy/ma/core.py:510, in _check_fill_value(fill_value, ndtype)
    509 try:
--> 510     fill_value = np.asarray(fill_value, dtype=ndtype)
    511 except (OverflowError, ValueError) as e:
    512     # Raise TypeError instead of OverflowError or ValueError.
    513     # OverflowError is seldom used, and the real problem here is
    514     # that the passed fill_value is not compatible with the ndtype.

ValueError: invalid literal for int() with base 10: np.str_('N/A')

The above exception was the direct cause of the following exception:

TypeError                                 Traceback (most recent call last)
File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/column.py:1338, in Column.__repr__(self)
   1337 def __repr__(self):
-> 1338     return self._base_repr_(html=False)

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/column.py:1326, in Column._base_repr_(self, html)
   1322     from astropy.utils.xml.writer import xml_escape
   1324     descr = xml_escape(descr)
-> 1326 data_lines, outs = self._formatter._pformat_col(
   1327     self, show_name=False, show_unit=False, show_length=False, html=html
   1328 )
   1330 out = descr + "\n".join(data_lines)
   1332 return out

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/pprint.py:295, in TableFormatter._pformat_col(self, col, max_lines, show_name, show_unit, show_dtype, show_length, html, align)
    283 col_strs_iter = self._pformat_col_iter(
    284     col,
    285     max_lines,
   (...)    290     outs=outs,
    291 )
    293 # Replace tab and newline with text representations so they display nicely.
    294 # Newline in particular is a problem in a multicolumn table.
--> 295 col_strs = [
    296     val.replace("\t", "\\t").replace("\n", "\\n") for val in col_strs_iter
    297 ]
    298 if len(col_strs) > 0:
    299     col_width = max(len(x) for x in col_strs)

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/pprint.py:562, in TableFormatter._pformat_col_iter(self, col, max_lines, show_name, show_unit, outs, show_dtype, show_length)
    560 else:
    561     try:
--> 562         yield format_col_str(idx)
    563     except ValueError:
    564         raise ValueError(
    565             f'Unable to parse format string "{col_format}" for '
    566             f'entry "{col[idx]}" in column "{col.info.name}" '
   (...)    569             "for possible format specifications."
    570         )

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/pprint.py:522, in TableFormatter._pformat_col_iter.<locals>.format_col_str(idx)
    520 def format_col_str(idx):
    521     if not multidims:
--> 522         return format_func(col_format, col if is_scalar else col[idx])
    524     # Prevents columns like Column(data=[[(1,)],[(2,)]], name='a')
    525     # with shape (n,1,...,1) from being printed as if there was
    526     # more than one element in a row
    527     if multidims_all_ones:

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/_column_mixins.pyx:89, in astropy.table._column_mixins._MaskedColumnGetitemShim.__getitem__()
     87 cdef class _MaskedColumnGetitemShim(_ColumnGetitemShim):
     88     def __getitem__(self, item):
---> 89         return base_getitem(self, item, masked_column_getitem)

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/_column_mixins.pyx:59, in astropy.table._column_mixins.base_getitem()
     57     return self.data[item]
     58 
---> 59 value = getitem(self, item)
     60 
     61 try:

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/_column_mixins.pyx:83, in astropy.table._column_mixins.masked_column_getitem()
     81 
     82 cdef inline object masked_column_getitem(object self, object item):
---> 83     value = MaskedArray.__getitem__(self, item)
     84     return self._copy_attrs_slice(value)
     85 

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/numpy/ma/core.py:3288, in MaskedArray.__getitem__(self, indx)
   3278 """
   3279 x.__getitem__(y) <==> x[y]
   3280 
   3281 Return the item described by i, as a masked array.
   3282 
   3283 """
   3284 # We could directly use ndarray.__getitem__ on self.
   3285 # But then we would have to modify __array_finalize__ to prevent the
   3286 # mask of being reshaped if it hasn't been set up properly yet
   3287 # So it's easier to stick to the current version
-> 3288 dout = self.data[indx]
   3289 _mask = self._mask
   3291 def _is_scalar(m):

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/astropy/table/column.py:1734, in MaskedColumn.data(self)
   1731 @property
   1732 def data(self):
   1733     """The plain MaskedArray data held by this column."""
-> 1734     out = self.view(np.ma.MaskedArray)
   1735     # By default, a MaskedArray view will set the _baseclass to be the
   1736     # same as that of our own class, i.e., BaseColumn.  Since we want
   1737     # to return a plain MaskedArray, we reset the baseclass accordingly.
   1738     out._baseclass = np.ndarray

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/numpy/ma/core.py:3264, in MaskedArray.view(self, dtype, type, fill_value)
   3261     type = dtype
   3262     dtype = None
-> 3264 output = super().view(*[a for a in (dtype, type) if a is not None])
   3266 # Make sure to reset the _fill_value if needed
   3267 if getattr(output, '_fill_value', None) is not None:

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/numpy/ma/core.py:3138, in MaskedArray.__array_finalize__(self, obj)
   3136 # Finalize the fill_value
   3137 if self._fill_value is not None:
-> 3138     self._fill_value = _check_fill_value(self._fill_value, self.dtype)
   3139 elif self.dtype.names is not None:
   3140     # Finalize the default fill_value for structured arrays
   3141     self._fill_value = _check_fill_value(None, self.dtype)

File ~/miniconda3/envs/euclid/lib/python3.12/site-packages/numpy/ma/core.py:516, in _check_fill_value(fill_value, ndtype)
    511     except (OverflowError, ValueError) as e:
    512         # Raise TypeError instead of OverflowError or ValueError.
    513         # OverflowError is seldom used, and the real problem here is
    514         # that the passed fill_value is not compatible with the ndtype.
    515         err_msg = "Cannot convert fill_value %s to dtype %s"
--> 516         raise TypeError(err_msg % (fill_value, ndtype)) from e
    517 return np.array(fill_value)

TypeError: Cannot convert fill_value N/A to dtype int64

In [34]: np.strings.find(col.data, "foo")
Out[34]: 
masked_array(data=[ 0, -1, -1],
             mask=False,
       fill_value=np.str_('N/A'))

import astropy
astropy.system_info()