jonded94 opened a new pull request, #47601:
URL: https://github.com/apache/arrow/pull/47601
### Rationale for this change
In Python, `pyarrow.Schema` before was not hashable when it has `metadata`
set.
```
>>> import pyarrow
>>> pyarrow.schema([], metadata={b"1": b"1"})
-- schema metadata --
1: '1'
>>> schema = pyarrow.schema([], metadata={b"1": b"1"})
>>> hash(schema)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "pyarrow/types.pxi", line 2921, in pyarrow.lib.Schema.__hash__
TypeError: unhashable type: 'dict'
```
This is because the metadata (which is a dict) was tried to be hashed as-is,
which doesn't work.
### What changes are included in this PR?
Slightly change how hashes are computed for Schema, by converting the
`dict[str, str]` to the frozenset of key- and value tuples.
For reference, this is faster than computing the hash of a sorted tuple of
key- and value tuples (https://stackoverflow.com/a/6014481/10070873).
### Are these changes tested?
Yes.
### Are there any user-facing changes?
Besides that `Schema` now correctly is hashable, no.
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