feat(polars): accept list of CSVs to read_csv (#9232)

Polars now accepts a list of CSVs to `scan_csv` so we can expose this to
end-users.

A few caveats:
- it doesn't accept lists of globs, or lists of compressed CSVs, so we
  flatten the list of paths if it only has one element in case it is a
  glob or csv.gz

Fixes #9230

ibis/backends/duckdb/__init__.py

@@ -38,13 +38,6 @@
     from fsspec import AbstractFileSystem
 
 
-def normalize_filenames(source_list):
-    # Promote to list
-    source_list = util.promote_list(source_list)
-
-    return list(map(util.normalize_filename, source_list))
-
-
 _UDF_INPUT_TYPE_MAPPING = {
     InputType.PYARROW: duckdb.functional.ARROW,
     InputType.PYTHON: duckdb.functional.NATIVE,
@@ -649,7 +642,7 @@ def read_json(
             table_name,
             sg.select(STAR).from_(
                 self.compiler.f.read_json_auto(
-                    normalize_filenames(source_list), *options
+                    util.normalize_filenames(source_list), *options
                 )
             ),
         )
@@ -682,7 +675,7 @@ def read_csv(
             The just-registered table
 
         """
-        source_list = normalize_filenames(source_list)
+        source_list = util.normalize_filenames(source_list)
 
         if not table_name:
             table_name = util.gen_name("read_csv")
@@ -807,7 +800,7 @@ def read_parquet(
             The just-registered table
 
         """
-        source_list = normalize_filenames(source_list)
+        source_list = util.normalize_filenames(source_list)
 
         table_name = table_name or util.gen_name("read_parquet")
 
@@ -910,7 +903,7 @@ def read_delta(
             The just-registered table.
 
         """
-        source_table = normalize_filenames(source_table)[0]
+        source_table = util.normalize_filenames(source_table)[0]
 
         table_name = table_name or util.gen_name("read_delta")
 

ibis/backends/polars/__init__.py

@@ -22,7 +22,7 @@
 from ibis.backends.sql.dialects import Polars
 from ibis.expr.rewrites import lower_stringslice
 from ibis.formats.polars import PolarsSchema
-from ibis.util import gen_name, normalize_filename
+from ibis.util import gen_name, normalize_filename, normalize_filenames
 
 if TYPE_CHECKING:
     from collections.abc import Iterable
@@ -158,7 +158,10 @@ def sql(
         return self.table(name)
 
     def read_csv(
-        self, path: str | Path, table_name: str | None = None, **kwargs: Any
+        self,
+        path: str | Path | list[str | Path] | tuple[str | Path],
+        table_name: str | None = None,
+        **kwargs: Any,
     ) -> ir.Table:
         """Register a CSV file as a table.
 
@@ -180,16 +183,20 @@ def read_csv(
             The just-registered table
 
         """
-        path = normalize_filename(path)
+        source_list = normalize_filenames(path)
+        # Flatten the list if there's only one element because Polars
+        # can't handle glob strings, or compressed CSVs in a single-element list
+        if len(source_list) == 1:
+            source_list = source_list[0]
         table_name = table_name or gen_name("read_csv")
         try:
-            table = pl.scan_csv(path, **kwargs)
+            table = pl.scan_csv(source_list, **kwargs)
             # triggers a schema computation to handle compressed csv inference
             # and raise a compute error
             table.schema  # noqa: B018
         except pl.exceptions.ComputeError:
             # handles compressed csvs
-            table = pl.read_csv(path, **kwargs)
+            table = pl.read_csv(source_list, **kwargs)
 
         self._add_table(table_name, table)
         return self.table(table_name)

ibis/backends/tests/test_register.py

@@ -74,7 +74,7 @@ def gzip_csv(data_dir, tmp_path):
             "fancy_stones2",
             id="multi_csv",
             marks=pytest.mark.notyet(
-                ["polars", "datafusion"],
+                ["datafusion"],
                 reason="doesn't accept multiple files to scan or read",
             ),
         ),

ibis/util.py

@@ -509,6 +509,13 @@ def _absolufy_paths(name):
     return source
 
 
+def normalize_filenames(source_list):
+    # Promote to list
+    source_list = promote_list(source_list)
+
+    return list(map(normalize_filename, source_list))
+
+
 def gen_name(namespace: str) -> str:
     """Create a unique identifier."""
     uid = base64.b32encode(uuid.uuid4().bytes).decode().rstrip("=").lower()