feat(tbl): add tbl function for pandas and sqla

siuba/dply/verbs.py

@@ -31,7 +31,8 @@
         "join", "inner_join", "full_join", "left_join", "right_join", "semi_join", "anti_join",
         # TODO: move to vectors
         "if_else", "case_when",
-        "collect", "show_query"
+        "collect", "show_query",
+        "tbl",
         )
 
 __all__ = [*DPLY_FUNCTIONS, "Pipeable", "pipe"]
@@ -2291,6 +2292,31 @@ def _extract_gdf(__data, *args, **kwargs):
     return out.groupby(groupings)
 
 
+# tbl ----
+from siuba.siu._databackend import SqlaEngine
+
+@singledispatch2((pd.DataFrame, DataFrameGroupBy))
+def tbl(src, *args, **kwargs):
+    return src
+
+
+@tbl.register
+def _tbl_sqla(src: SqlaEngine, table_name, columns=None):
+    from siuba.sql import LazyTbl
+
+    if src.dialect.name == "duckdb" and isinstance(columns, pd.DataFrame):
+        src.execute("register", (table_name, columns))
+
+    return LazyTbl(src, table_name)
+
+
+tbl.register(object)
+def _tbl(__data, *args, **kwargs):
+    raise NotImplementedError(
+        f"Unsupported type {type(__data)}. "
+        "Note that tbl currently cannot be used in a pipe."
+    )
+
 # Install Siu =================================================================
 
 install_pd_siu()

siuba/siu/_databackend.py

@@ -0,0 +1,52 @@
+"""
+This module allows you to check types (e.g. using isinstance) without importing them.
+
+Note that this is copied from https://github.com/machow/databackend
+
+"""
+
+import sys
+import importlib
+
+from abc import ABCMeta
+
+
+def _load_class(mod_name: str, cls_name: str):
+    mod = importlib.import_module(mod_name)
+    return getattr(mod, cls_name)
+
+
+class _AbstractBackendMeta(ABCMeta):
+    def __new__(mcls, clsname, bases, attrs):
+        cls = super().__new__(mcls, clsname, bases, attrs)
+        if not hasattr(cls, "_backends"):
+            cls._backends = []
+        return cls
+
+    def register_backend(cls, mod_name: str, cls_name: str):
+        cls._backends.append((mod_name, cls_name))
+        cls._abc_caches_clear()
+
+
+class AbstractBackend(metaclass=_AbstractBackendMeta):
+    @classmethod
+    def __subclasshook__(cls, subclass):
+        for mod_name, cls_name in cls._backends:
+            if mod_name not in sys.modules:
+                # module isn't loaded, so it can't be the subclass
+                # we don't want to import the module to explicitly run the check
+                # so skip here.
+                continue
+            else:
+                target_cls = _load_class(mod_name, cls_name)
+                if issubclass(target_cls, subclass):
+                    return True
+
+        return NotImplemented
+
+
+# Implementations -------------------------------------------------------------
+
+class SqlaEngine(AbstractBackend): pass
+
+SqlaEngine.register_backend("sqlalchemy.engine", "Engine")