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FutureWarning if a table cell is a numpy array #287

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alugowski opened this issue Aug 26, 2023 · 1 comment · May be fixed by #288
Open

FutureWarning if a table cell is a numpy array #287

alugowski opened this issue Aug 26, 2023 · 1 comment · May be fixed by #288

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@alugowski
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import numpy as np
from tabulate import tabulate

data = [[np.ones(1)]]

print(tabulate(data))

Yields this warning from numpy:

/Users/enos/temp/venv/lib/python3.10/site-packages/tabulate/__init__.py:107: FutureWarning: elementwise comparison failed; returning scalar instead, but in the future will perform elementwise comparison
  (len(row) >= 1 and row[0] == SEPARATING_LINE)
-
1
-

The cause is that the line detection function,

def _is_separating_line(row):
    row_type = type(row)
    is_sl = (row_type == list or row_type == str) and (
        (len(row) >= 1 and row[0] == SEPARATING_LINE)
        or (len(row) >= 2 and row[1] == SEPARATING_LINE)
    )
    return is_sl

performs the == operation. This is generally correct, but with numpy (and also other array packages) an == does elementwise comparisons and not object-level. This should still yield the correct answer, just inefficiently and numpy in particular emits that warning.

The fix is simple. Replace the == with is:

        (len(row) >= 1 and row[0] is SEPARATING_LINE)
        or (len(row) >= 2 and row[1] is SEPARATING_LINE)

The is should also be a tiny bit faster, too.
@alugowski
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Correction, this is now an error in the newest numpy:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

The fix is the same.

alugowski added a commit to alugowski/python-tabulate that referenced this issue Aug 28, 2023
@alugowski
Fix separating line detection with ndarray values
392be0f 
This code:
```
import numpy as np
from tabulate import tabulate

data = [[np.ones(1)]]

print(tabulate(data))
```

Throws a `FutureWarning` or a `ValueError` due to the comparison with `SEPARATING_LINE`. 


Fixes astanin#287
@alugowski alugowski linked a pull request Aug 28, 2023 that will close this issue
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Fix separating line detection with ndarray values alugowski/python-tabulate
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@alugowski