ENH: make "closed" part of IntervalDtype

doc/source/whatsnew/v1.3.0.rst

@@ -122,7 +122,7 @@ Other API changes
 
 Deprecations
 ~~~~~~~~~~~~
-
+- Deprecated construction of :class:`IntervalDtype` without specifying ``closed`` (:issue:`38394`)
 -
 -
 

pandas/conftest.py

@@ -703,8 +703,8 @@ def float_frame():
 # ----------------------------------------------------------------
 @pytest.fixture(
     params=[
-        (Interval(left=0, right=5), IntervalDtype("int64")),
-        (Interval(left=0.1, right=0.5), IntervalDtype("float64")),
+        (Interval(left=0, right=5), IntervalDtype("int64", "right")),
+        (Interval(left=0.1, right=0.5), IntervalDtype("float64", "right")),
         (Period("2012-01", freq="M"), "period[M]"),
         (Period("2012-02-01", freq="D"), "period[D]"),
         (

pandas/core/arrays/_arrow_utils.py

@@ -127,7 +127,7 @@ def __hash__(self):
         def to_pandas_dtype(self):
             import pandas as pd
 
-            return pd.IntervalDtype(self.subtype.to_pandas_dtype())
+            return pd.IntervalDtype(self.subtype.to_pandas_dtype(), self.closed)
 
     # register the type with a dummy instance
     _interval_type = ArrowIntervalType(pyarrow.int64(), "left")

pandas/core/arrays/interval.py

@@ -146,7 +146,7 @@
     >>> pd.arrays.IntervalArray([pd.Interval(0, 1), pd.Interval(1, 5)])
     <IntervalArray>
     [(0, 1], (1, 5]]
-    Length: 2, closed: right, dtype: interval[int64]
+    Length: 2, closed: right, dtype: interval[int64, right]
 
     It may also be constructed using one of the constructor
     methods: :meth:`IntervalArray.from_arrays`,
@@ -213,6 +213,9 @@ def _simple_new(
     ):
         result = IntervalMixin.__new__(cls)
 
+        if closed is None and isinstance(dtype, IntervalDtype):
+            closed = dtype.closed
+
         closed = closed or "right"
         left = ensure_index(left, copy=copy)
         right = ensure_index(right, copy=copy)
@@ -227,6 +230,12 @@ def _simple_new(
                 left = left.astype(dtype.subtype)
                 right = right.astype(dtype.subtype)
 
+            if dtype.closed is None:
+                # possibly loading an old pickle
+                dtype = IntervalDtype(dtype.subtype, closed)
+            elif closed != dtype.closed:
+                raise ValueError("closed keyword does not match dtype.closed")
+
         # coerce dtypes to match if needed
         if is_float_dtype(left) and is_integer_dtype(right):
             right = right.astype(left.dtype)
@@ -268,9 +277,11 @@ def _simple_new(
             # If these share data, then setitem could corrupt our IA
             right = right.copy()
 
+        dtype = IntervalDtype(left.dtype, closed=closed)
+        result._dtype = dtype
+
         result._left = left
         result._right = right
-        result._closed = closed
         if verify_integrity:
             result._validate()
         return result
@@ -330,7 +341,7 @@ def _from_factorized(cls, values, original):
         >>> pd.arrays.IntervalArray.from_breaks([0, 1, 2, 3])
         <IntervalArray>
         [(0, 1], (1, 2], (2, 3]]
-        Length: 3, closed: right, dtype: interval[int64]
+        Length: 3, closed: right, dtype: interval[int64, right]
         """
             ),
         }
@@ -399,7 +410,7 @@ def from_breaks(cls, breaks, closed="right", copy=False, dtype=None):
         >>> pd.arrays.IntervalArray.from_arrays([0, 1, 2], [1, 2, 3])
         <IntervalArray>
         [(0, 1], (1, 2], (2, 3]]
-        Length: 3, closed: right, dtype: interval[int64]
+        Length: 3, closed: right, dtype: interval[int64, right]
         """
             ),
         }
@@ -456,7 +467,7 @@ def from_arrays(cls, left, right, closed="right", copy=False, dtype=None):
         >>> pd.arrays.IntervalArray.from_tuples([(0, 1), (1, 2)])
         <IntervalArray>
         [(0, 1], (1, 2]]
-        Length: 2, closed: right, dtype: interval[int64]
+        Length: 2, closed: right, dtype: interval[int64, right]
         """
             ),
         }
@@ -534,7 +545,7 @@ def _shallow_copy(self, left, right):
 
     @property
     def dtype(self):
-        return IntervalDtype(self.left.dtype)
+        return self._dtype
 
     @property
     def nbytes(self) -> int:
@@ -1155,7 +1166,7 @@ def mid(self):
         >>> intervals
         <IntervalArray>
         [(0, 1], (1, 3], (2, 4]]
-        Length: 3, closed: right, dtype: interval[int64]
+        Length: 3, closed: right, dtype: interval[int64, right]
         """
             ),
         }
@@ -1184,7 +1195,7 @@ def closed(self):
         Whether the intervals are closed on the left-side, right-side, both or
         neither.
         """
-        return self._closed
+        return self.dtype.closed
 
     _interval_shared_docs["set_closed"] = textwrap.dedent(
         """
@@ -1219,11 +1230,11 @@ def closed(self):
         >>> index
         <IntervalArray>
         [(0, 1], (1, 2], (2, 3]]
-        Length: 3, closed: right, dtype: interval[int64]
+        Length: 3, closed: right, dtype: interval[int64, right]
         >>> index.set_closed('both')
         <IntervalArray>
         [[0, 1], [1, 2], [2, 3]]
-        Length: 3, closed: both, dtype: interval[int64]
+        Length: 3, closed: both, dtype: interval[int64, both]
         """
             ),
         }
@@ -1282,7 +1293,7 @@ def __array__(self, dtype=None) -> np.ndarray:
         left = self._left
         right = self._right
         mask = self.isna()
-        closed = self._closed
+        closed = self.closed
 
         result = np.empty(len(left), dtype=object)
         for i in range(len(left)):
@@ -1422,7 +1433,7 @@ def repeat(self, repeats, axis=None):
         >>> intervals
         <IntervalArray>
         [(0, 1], (1, 3], (2, 4]]
-        Length: 3, closed: right, dtype: interval[int64]
+        Length: 3, closed: right, dtype: interval[int64, right]
         """
             ),
         }

pandas/core/dtypes/cast.py

@@ -793,7 +793,7 @@ def infer_dtype_from_scalar(val, pandas_dtype: bool = False) -> Tuple[DtypeObj,
             dtype = PeriodDtype(freq=val.freq)
         elif lib.is_interval(val):
             subtype = infer_dtype_from_scalar(val.left, pandas_dtype=True)[0]
-            dtype = IntervalDtype(subtype=subtype)
+            dtype = IntervalDtype(subtype=subtype, closed=val.closed)
 
     return dtype, val
 

pandas/core/dtypes/dtypes.py

@@ -15,6 +15,7 @@
     Union,
     cast,
 )
+import warnings
 
 import numpy as np
 import pytz
@@ -1002,37 +1003,75 @@ class IntervalDtype(PandasExtensionDtype):
 
     Examples
     --------
-    >>> pd.IntervalDtype(subtype='int64')
-    interval[int64]
+    >>> pd.IntervalDtype(subtype='int64', closed='both')
+    interval[int64, both]
     """
 
     name = "interval"
     kind: str_type = "O"
     str = "|O08"
     base = np.dtype("O")
     num = 103
-    _metadata = ("subtype",)
-    _match = re.compile(r"(I|i)nterval\[(?P<subtype>.+)\]")
+    _metadata = (
+        "subtype",
+        "closed",
+    )
+    _match = re.compile(
+        r"(I|i)nterval\[(?P<subtype>[^,]+)(, (?P<closed>(right|left|both|neither)))?\]"
+    )
     _cache: Dict[str_type, PandasExtensionDtype] = {}
 
-    def __new__(cls, subtype=None):
+    def __new__(cls, subtype=None, closed: Optional[str_type] = None):
         from pandas.core.dtypes.common import is_string_dtype, pandas_dtype
 
+        if closed is not None and closed not in {"right", "left", "both", "neither"}:
+            raise ValueError("closed must be one of 'right', 'left', 'both', 'neither'")
+
         if isinstance(subtype, IntervalDtype):
+            if closed is not None and closed != subtype.closed:
+                raise ValueError(
+                    "dtype.closed and 'closed' do not match. "
+                    "Try IntervalDtype(dtype.subtype, closed) instead."
+                )
             return subtype
         elif subtype is None:
             # we are called as an empty constructor
             # generally for pickle compat
             u = object.__new__(cls)
             u._subtype = None
+            u._closed = closed
             return u
         elif isinstance(subtype, str) and subtype.lower() == "interval":
             subtype = None
         else:
             if isinstance(subtype, str):
                 m = cls._match.search(subtype)
                 if m is not None:
-                    subtype = m.group("subtype")
+                    gd = m.groupdict()
+                    subtype = gd["subtype"]
+                    if gd.get("closed", None) is not None:
+                        if closed is not None:
+                            if closed != gd["closed"]:
+                                raise ValueError(
+                                    "'closed' keyword does not match value "
+                                    "specified in dtype string"
+                                )
+                        closed = gd["closed"]
+                    elif closed is not None:
+                        # user passed eg. IntervalDtype("interval[int64]", "left")
+                        pass
+                    else:
+                        warnings.warn(
+                            "Constructing an IntervalDtype from a string without "
+                            "specifying 'closed' is deprecated and will raise in "
+                            "a future version. "
+                            f"Use e.g. 'interval[{subtype}, left]'. "
+                            "Defaulting to closed='right'.",
+                            FutureWarning,
+                            stacklevel=2,
+                        )
+                        # default to "right"
+                        closed = "right"
 
             try:
                 subtype = pandas_dtype(subtype)
@@ -1047,14 +1086,32 @@ def __new__(cls, subtype=None):
             )
             raise TypeError(msg)
 
+        if closed is None and subtype is not None:
+            warnings.warn(
+                "Constructing an IntervalDtype without "
+                "specifying 'closed' is deprecated and will raise in "
+                "a future version. "
+                "Use e.g. IntervalDtype(np.int64, 'left'). "
+                "Defaulting to closed='right'.",
+                FutureWarning,
+                stacklevel=2,
+            )
+            closed = "right"
+
+        key = str(subtype) + str(closed)
         try:
-            return cls._cache[str(subtype)]
+            return cls._cache[key]
         except KeyError:
             u = object.__new__(cls)
             u._subtype = subtype
-            cls._cache[str(subtype)] = u
+            u._closed = closed
+            cls._cache[key] = u
             return u
 
+    @property
+    def closed(self):
+        return self._closed
+
     @property
     def subtype(self):
         """
@@ -1104,7 +1161,7 @@ def type(self):
     def __str__(self) -> str_type:
         if self.subtype is None:
             return "interval"
-        return f"interval[{self.subtype}]"
+        return f"interval[{self.subtype}, {self.closed}]"
 
     def __hash__(self) -> int:
         # make myself hashable
@@ -1118,6 +1175,8 @@ def __eq__(self, other: Any) -> bool:
         elif self.subtype is None or other.subtype is None:
             # None should match any subtype
             return True
+        elif self.closed != other.closed:
+            return False
         else:
             from pandas.core.dtypes.common import is_dtype_equal
 
@@ -1129,6 +1188,17 @@ def __setstate__(self, state):
         # pickle -> need to set the settable private ones here (see GH26067)
         self._subtype = state["subtype"]
 
+        # backward-compat older pickles won't have "closed" key
+        self._closed = state.pop("closed", None)
+        if self._closed is None:
+            warnings.warn(
+                "Unpickled legacy IntervalDtype does not specify 'closed' "
+                "attribute.  Set dtype._closed to one of 'left', 'right', 'both', "
+                "'neither' before using this IntervalDtype object.",
+                UserWarning,
+                stacklevel=2,
+            )
+
     @classmethod
     def is_dtype(cls, dtype: object) -> bool:
         """
@@ -1175,11 +1245,15 @@ def __from_arrow__(
     def _get_common_dtype(self, dtypes: List[DtypeObj]) -> Optional[DtypeObj]:
         # NB: this doesn't handle checking for closed match
         if not all(isinstance(x, IntervalDtype) for x in dtypes):
+            return None
+
+        closed = cast("IntervalDtype", dtypes[0]).closed
+        if not all(cast("IntervalDtype", x).closed == closed for x in dtypes):
             return np.dtype(object)
 
         from pandas.core.dtypes.cast import find_common_type
 
         common = find_common_type([cast("IntervalDtype", x).subtype for x in dtypes])
         if common == object:
             return np.dtype(object)
-        return IntervalDtype(common)
+        return IntervalDtype(common, closed=closed)