Nishuuzz opened a new pull request, #51753:
URL: https://github.com/apache/arrow/pull/51753
`pa.show_info()` prints its Compression Codecs section from a hardcoded list:
```python
codecs = ["brotli", "bz2", "gzip", "lz4_frame", "lz4", "snappy", "zstd"]
```
That list has drifted from `_ensure_compression()` in io.pxi, which is what
actually decides which names work. Two things fall out of it:
- `lz4` and `lz4_frame` both map to `CCompressionType_LZ4_FRAME`, so the
same codec is reported twice under two names.
- `lz4_raw` maps to `CCompressionType_LZ4` and is a separate codec, but it
is not listed at all, even though `pa.Codec.is_available('lz4_raw')` is True.
So seven lines get printed for six codecs, and the one codec that is missing
is a real one. Before:
```
Compression Codecs:
brotli : Enabled
bz2 : Enabled
gzip : Enabled
lz4_frame : Enabled
lz4 : Enabled
snappy : Enabled
zstd : Enabled
```
After:
```
Compression Codecs:
brotli : Enabled
bz2 : Enabled
gzip : Enabled
lz4 : Enabled
lz4_raw : Enabled
snappy : Enabled
zstd : Enabled
```
`lz4` is kept as the name for the frame codec since that is the one the
docstrings lead with (`'lz4' (or 'lz4_frame')`).
I checked this by applying the same change to an installed pyarrow and
reading the output back, and by walking every name `_ensure_compression()`
accepts to confirm which map onto the same C++ enum value. `show_info()` has no
test coverage today and its output is a diagnostic print, so I have not added
one, but I am happy to if you would prefer it pinned.
Found while comparing hardcoded Python lists against their C++ counterparts,
the same way GH-50847 turned up.
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