8000 Add _format_str mapping to interchange protocol by AlenkaF · Pull Request #62 · data-apis/dataframe-api · GitHub
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Add _format_str mapping to interchange protocol #62

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Add _format_str mapping to interchange protocol #62

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e429a50
Added _format_str: mapping NumPy to Arrow format strings
AlenkaF Sep 7, 2021
1dd21bb
Added test for _format_str
AlenkaF Sep 7, 2021
8f43391
Fix typo
kgryte Sep 7, 2021
8206620
Fix incomplete test
AlenkaF Sep 8, 2021
83c22d6
Merge branch 'format_strings' of https://github.com/AlenkaF/dataframe…
AlenkaF Sep 8, 2021
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Added _format_str: mapping NumPy to Arrow format strings
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@AlenkaF
AlenkaF committed Sep 7, 2021
commit e429a5063b465b228405ecd6e0c08af5d6ff3aaf
24 changes: 23 additions & 1 deletion protocol/pandas_implementation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -435,10 +435,32 @@ def _dtype_from_pandasdtype(self, dtype) -> Tuple[enum.IntEnum, int, str, str]:
raise NotImplementedError(f"Data type {dtype} not handled yet")

bitwidth = dtype.itemsize * 8
format_str = dtype.str
format_str = self._format_str(dtype.str)
endianness = dtype.byteorder if not kind == _k.CATEGORICAL else '='
return (kind, bitwidth, format_str, endianness)

def _format_str(self, format_str) -> str:
"""
Mapping of NumPy formt strings to
Apache Arrow C Data Interface format strings.
'O' categorical mapped as 'U': large utf-8 string for now
"""
_ints = {8: 'c', 16: 's', 32: 'i', 64: 'l'}
_uints = {8: 'C', 16: 'S', 32: 'I', 64: 'L'}
_floats = {16: 'e', 32: 'f', 64: 'g'}
_np_dtypes = {'i': _ints, 'u': _uints, 'f': _floats, 'b': {8: 'b'}, 'O': {64: 'U'}}

dt = np.dtype(format_str)
if dt.byteorder == '>':
raise ValueError(f"Big-endian not supported by exchange"
"protocol")

arrow_format_str = _np_dtypes.get(dt.kind, {}).get(dt.itemsize*8)

if arrow_format_str is None:
raise NotImplementedError(f"Format string {format_str} not handled yet")

return arrow_format_str

@property
def describe_categorical(self) -> Dict[str, Any]:
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