feat(selectors): Add All and None_ to complete selector group (#46)

* feat(selectors): Add All and None_ selectors

* Import All and None_ from __init__

* Update CHANGELOG [skip ci]

* Re-flow CHANGELOG

CHANGELOG.rst

@@ -7,6 +7,8 @@ v0.4.0 (2023-12-12)
 ------------------------------------------------------------
 * **BREAKING** :mod:`accessors` is imported implicitly. User code does not need to
   import it any longer :pull:`45`
+* Add :attr:`~selectors.All` and :attr:`~selectors.None_` completing selector group
+  :pull:`46`
 * Fix type hints of function :func:`~core.aggregatelevel` :pull:`44`
 * Switch from black to ruff for formatting and update pre-commit versions :pull:`43`
 

src/pandas_indexing/__init__.py

@@ -21,7 +21,7 @@
     to_tidy,
     uniquelevel,
 )
-from .selectors import isin, ismatch
+from .selectors import All, None_, isin, ismatch
 from .units import convert_unit, dequantify, quantify, set_openscm_registry_as_default
 
 

src/pandas_indexing/selectors.py

@@ -26,9 +26,13 @@ def __invert__(self):
         return Not(self)
 
     def __and__(self, other):
+        if isinstance(other, Special):
+            return other & self
         return And(self, maybe_const(other))
 
     def __or__(self, other):
+        if isinstance(other, Special):
+            return other | self
         return Or(self, maybe_const(other))
 
     __rand__ = __and__
@@ -69,6 +73,48 @@ def __call__(self, df):
         return ~self.a.__call__(df)
 
 
+class Special(Selector):
+    pass
+
+
+@define
+class AllSelector(Special):
+    def __invert__(self):
+        return NoneSelector()
+
+    def __and__(self, other):
+        return other
+
+    def __or__(self, other):
+        return self
+
+    def __call__(self, df):
+        return Series(True, df.index)
+
+
+@define
+class NoneSelector(Special):
+    def __invert__(self):
+        return AllSelector()
+
+    def __and__(self, other):
+        return self
+
+    def __or__(self, other):
+        return other
+
+    __rand__ = __and__
+    __ror__ = __or__
+
+    def __call__(self, df):
+        return Series(False, df.index)
+
+
+# Singletons for easy access
+All = AllSelector()
+None_ = NoneSelector()
+
+
 @define
 class Isin(Selector):
     filters: Mapping[str, Any]

tests/test_selectors.py

@@ -5,7 +5,16 @@
 from pandas.testing import assert_frame_equal, assert_series_equal
 
 from pandas_indexing import isin, ismatch
-from pandas_indexing.selectors import And, Const, Isin, Ismatch, Not, Or
+from pandas_indexing.selectors import (
+    AllSelector,
+    And,
+    Const,
+    Isin,
+    Ismatch,
+    NoneSelector,
+    Not,
+    Or,
+)
 
 
 def test_isin_mseries(mseries: Series):
@@ -57,3 +66,23 @@ def test_ismatch_explicitly_given(sdf):
     assert_series_equal(
         ismatch(sdf.columns, ["o*"]), Series([True, False], sdf.columns)
     )
+
+
+def test_all_none(sdf):
+    assert isinstance(~AllSelector(), NoneSelector)
+    assert isinstance(~NoneSelector(), AllSelector)
+
+    sel = isin(str="bar")
+
+    assert isinstance(sel | AllSelector(), AllSelector)
+    assert isinstance(AllSelector() | sel, AllSelector)
+    assert sel & AllSelector() == sel
+    assert AllSelector() & sel == sel
+
+    assert sel | NoneSelector() == sel
+    assert NoneSelector() | sel == sel
+    assert isinstance(sel & NoneSelector(), NoneSelector)
+    assert isinstance(NoneSelector() & sel, NoneSelector)
+
+    assert_frame_equal(sdf.loc[AllSelector()], sdf)
+    assert_frame_equal(sdf.loc[NoneSelector()], sdf.iloc[[]])