Title: Handle 0-dim tensors in `cast_to_python_objects`
State: closed

Fix #5229 

Comments:
_The documentation is not available anymore as the PR was closed or merged._

<details>
<summary>Show benchmarks</summary>

PyArrow==6.0.0

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.010576 / 0.011353 (-0.000777) | 0.006010 / 0.011008 (-0.004998) | 0.109375 / 0.038508 (0.070867) | 0.037780 / 0.023109 (0.014670) | 0.381552 / 0.275898 (0.105654) | 0.446039 / 0.323480 (0.122559) | 0.009004 / 0.007986 (0.001019) | 0.005653 / 0.004328 (0.001324) | 0.087027 / 0.004250 (0.082776) | 0.040346 / 0.037052 (0.003293) | 0.398827 / 0.258489 (0.140338) | 0.407281 / 0.293841 (0.113440) | 0.051723 / 0.128546 (-0.076824) | 0.020254 / 0.075646 (-0.055392) | 0.376841 / 0.419271 (-0.042430) | 0.055505 / 0.043533 (0.011972) | 0.383464 / 0.255139 (0.128325) | 0.436130 / 0.283200 (0.152930) | 0.117403 / 0.141683 (-0.024280) | 1.569016 / 1.452155 (0.116862) | 1.889831 / 1.492716 (0.397115) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.297962 / 0.018006 (0.279956) | 0.683699 / 0.000490 (0.683210) | 0.000918 / 0.000200 (0.000718) | 0.000100 / 0.000054 (0.000045) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.026742 / 0.037411 (-0.010669) | 0.125293 / 0.014526 (0.110768) | 0.128769 / 0.176557 (-0.047787) | 0.179447 / 0.737135 (-0.557688) | 0.142032 / 0.296338 (-0.154306) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.588389 / 0.215209 (0.373180) | 5.943514 / 2.077655 (3.865859) | 2.631163 / 1.504120 (1.127043) | 1.865446 / 1.541195 (0.324252) | 2.055610 / 1.468490 (0.587120) | 1.090288 / 4.584777 (-3.494489) | 5.457151 / 3.745712 (1.711439) | 5.645614 / 5.269862 (0.375752) | 2.849492 / 4.565676 (-1.716184) | 0.140447 / 0.424275 (-0.283828) | 0.015421 / 0.007607 (0.007813) | 0.735528 / 0.226044 (0.509484) | 7.394097 / 2.268929 (5.125169) | 3.219714 / 55.444624 (-52.224911) | 2.504134 / 6.876477 (-4.372342) | 2.524291 / 2.142072 (0.382219) | 1.452776 / 4.805227 (-3.352452) | 0.256142 / 6.500664 (-6.244522) | 0.093809 / 0.075469 (0.018340) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.570046 / 1.841788 (-0.271742) | 17.360385 / 8.074308 (9.286077) | 20.750595 / 10.191392 (10.559203) | 0.218486 / 0.680424 (-0.461938) | 0.048527 / 0.534201 (-0.485674) | 0.549568 / 0.579283 (-0.029715) | 0.633993 / 0.434364 (0.199629) | 0.632585 / 0.540337 (0.092248) | 0.712817 / 1.386936 (-0.674119) |

</details>
PyArrow==latest

<details>
<summary>Show updated benchmarks!</summary>

### Benchmark: benchmark_array_xd.json

| metric | read_batch_formatted_as_numpy after write_array2d | read_batch_formatted_as_numpy after write_flattened_sequence | read_batch_formatted_as_numpy after write_nested_sequence | read_batch_unformated after write_array2d | read_batch_unformated after write_flattened_sequence | read_batch_unformated after write_nested_sequence | read_col_formatted_as_numpy after write_array2d | read_col_formatted_as_numpy after write_flattened_sequence | read_col_formatted_as_numpy after write_nested_sequence | read_col_unformated after write_array2d | read_col_unformated after write_flattened_sequence | read_col_unformated after write_nested_sequence | read_formatted_as_numpy after write_array2d | read_formatted_as_numpy after write_flattened_sequence | read_formatted_as_numpy after write_nested_sequence | read_unformated after write_array2d | read_unformated after write_flattened_sequence | read_unformated after write_nested_sequence | write_array2d | write_flattened_sequence | write_nested_sequence |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.010524 / 0.011353 (-0.000829) | 0.006307 / 0.011008 (-0.004701) | 0.129671 / 0.038508 (0.091162) | 0.038952 / 0.023109 (0.015842) | 0.421936 / 0.275898 (0.146038) | 0.489911 / 0.323480 (0.166431) | 0.007661 / 0.007986 (-0.000325) | 0.005430 / 0.004328 (0.001102) | 0.091851 / 0.004250 (0.087600) | 0.059755 / 0.037052 (0.022703) | 0.449810 / 0.258489 (0.191321) | 0.519498 / 0.293841 (0.225657) | 0.061644 / 0.128546 (-0.066902) | 0.018950 / 0.075646 (-0.056696) | 0.399149 / 0.419271 (-0.020122) | 0.067670 / 0.043533 (0.024137) | 0.441091 / 0.255139 (0.185952) | 0.459327 / 0.283200 (0.176128) | 0.122476 / 0.141683 (-0.019207) | 1.760129 / 1.452155 (0.307974) | 1.767945 / 1.492716 (0.275228) |

### Benchmark: benchmark_getitem\_100B.json

| metric | get_batch_of\_1024\_random_rows | get_batch_of\_1024\_rows | get_first_row | get_last_row |
|--------|---|---|---|---|
| new / old (diff) | 0.276675 / 0.018006 (0.258669) | 0.606798 / 0.000490 (0.606308) | 0.000449 / 0.000200 (0.000249) | 0.000078 / 0.000054 (0.000023) |

### Benchmark: benchmark_indices_mapping.json

| metric | select | shard | shuffle | sort | train_test_split |
|--------|---|---|---|---|---|
| new / old (diff) | 0.027762 / 0.037411 (-0.009649) | 0.108330 / 0.014526 (0.093805) | 0.134714 / 0.176557 (-0.041843) | 0.175666 / 0.737135 (-0.561470) | 0.134917 / 0.296338 (-0.161421) |

### Benchmark: benchmark_iterating.json

| metric | read 5000 | read 50000 | read_batch 50000 10 | read_batch 50000 100 | read_batch 50000 1000 | read_formatted numpy 5000 | read_formatted pandas 5000 | read_formatted tensorflow 5000 | read_formatted torch 5000 | read_formatted_batch numpy 5000 10 | read_formatted_batch numpy 5000 1000 | shuffled read 5000 | shuffled read 50000 | shuffled read_batch 50000 10 | shuffled read_batch 50000 100 | shuffled read_batch 50000 1000 | shuffled read_formatted numpy 5000 | shuffled read_formatted_batch numpy 5000 10 | shuffled read_formatted_batch numpy 5000 1000 |
|--------|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 0.676756 / 0.215209 (0.461547) | 6.746519 / 2.077655 (4.668864) | 2.660869 / 1.504120 (1.156750) | 2.273688 / 1.541195 (0.732494) | 2.392580 / 1.468490 (0.924090) | 1.127848 / 4.584777 (-3.456929) | 5.356499 / 3.745712 (1.610787) | 2.933006 / 5.269862 (-2.336855) | 1.872877 / 4.565676 (-2.692799) | 0.139504 / 0.424275 (-0.284771) | 0.013501 / 0.007607 (0.005894) | 0.749888 / 0.226044 (0.523843) | 8.157031 / 2.268929 (5.888103) | 3.627751 / 55.444624 (-51.816874) | 2.713152 / 6.876477 (-4.163324) | 2.934585 / 2.142072 (0.792512) | 1.376398 / 4.805227 (-3.428829) | 0.251537 / 6.500664 (-6.249127) | 0.083995 / 0.075469 (0.008526) |

### Benchmark: benchmark_map_filter.json

| metric | filter | map fast-tokenizer batched | map identity | map identity batched | map no-op batched | map no-op batched numpy | map no-op batched pandas | map no-op batched pytorch | map no-op batched tensorflow |
|--------|---|---|---|---|---|---|---|---|---|
| new / old (diff) | 1.635446 / 1.841788 (-0.206342) | 18.435807 / 8.074308 (10.361498) | 21.395291 / 10.191392 (11.203899) | 0.247238 / 0.680424 (-0.433186) | 0.030503 / 0.534201 (-0.503698) | 0.553096 / 0.579283 (-0.026187) | 0.597583 / 0.434364 (0.163219) | 0.594135 / 0.540337 (0.053797) | 0.673815 / 1.386936 (-0.713122) |

</details>
</details>

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