fix(backend): read the default backend setting in _default_backend

ibis/backends/tests/test_client.py

@@ -719,6 +719,16 @@ def test_create_from_in_memory_table(backend, con, t):
         assert tmp_name not in con.list_tables()
 
 
+def test_default_backend_option():
+    orig = ibis.options.default_backend
+    ibis.options.default_backend = ibis.pandas
+    try:
+        backend = ibis.config._default_backend()
+        assert backend.name == "pandas"
+    finally:
+        ibis.options.default_backend = orig
+
+
 def test_default_backend_no_duckdb(backend):
     # backend is used to ensure that this test runs in CI in the setting
     # where only the dependencies for a a given backend are installed

ibis/config.py

@@ -167,29 +167,19 @@ class Options(Config):
     pyspark: Optional[Config] = None
 
 
-_HAS_DUCKDB = True
-_DUCKDB_CON = None
-
-
 def _default_backend() -> Any:
-    global _HAS_DUCKDB, _DUCKDB_CON
-
-    if not _HAS_DUCKDB:
-        return None
-
-    if _DUCKDB_CON is not None:
-        return _DUCKDB_CON
+    if (backend := options.default_backend) is not None:
+        return backend
 
     try:
         import duckdb as _  # noqa: F401
     except ImportError:
-        _HAS_DUCKDB = False
         return None
 
     import ibis
 
-    _DUCKDB_CON = ibis.duckdb.connect(":memory:")
-    return _DUCKDB_CON
+    options.default_backend = con = ibis.duckdb.connect(":memory:")
+    return con
 
 
 options = Options()