Add Python bindings for time zone data (TZiF) reader

python/cudf/cudf/_lib/CMakeLists.txt

@@ -48,6 +48,7 @@ set(cython_sources
     string_casting.pyx
     strings_udf.pyx
     text.pyx
+    timezone.pyx
     transform.pyx
     transpose.pyx
     types.pyx

python/cudf/cudf/_lib/__init__.py

@@ -35,6 +35,7 @@
     strings,
     strings_udf,
     text,
+    timezone,
     transpose,
     unary,
 )

python/cudf/cudf/_lib/cpp/io/timezone.pxd

@@ -0,0 +1,15 @@
+# Copyright (c) 2020-2023, NVIDIA CORPORATION.
+
+from libcpp cimport bool
+from libcpp.memory cimport unique_ptr
+from libcpp.string cimport string
+
+from cudf._lib.cpp.libcpp.optional cimport optional
+from cudf._lib.cpp.table.table cimport table
+
+
+cdef extern from "cudf/timezone.hpp" namespace "cudf" nogil:
+    unique_ptr[table] make_timezone_transition_table(
+        optional[string] tzif_dir,
+        string timezone_name
+    ) except +

python/cudf/cudf/_lib/cpp/libcpp/optional.pxd

@@ -0,0 +1,50 @@
+# SPDX-FileCopyrightText: Copyright (c) 2023, NVIDIA CORPORATION &
+# AFFILIATES. All rights reserved.  SPDX-License-Identifier:
+# Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from libcpp cimport bool
+
+
+cdef extern from "<optional>" namespace "std" nogil:
+    cdef cppclass nullopt_t:
+        nullopt_t()
+
+    cdef nullopt_t nullopt
+
+    cdef cppclass optional[T]:
+        ctypedef T value_type
+        optional()
+        optional(nullopt_t)
+        optional(optional&) except +
+        optional(T&) except +
+        bool has_value()
+        T& value()
+        T& value_or[U](U& default_value)
+        void swap(optional&)
+        void reset()
+        T& emplace(...)
+        T& operator*()
+        optional& operator=(optional&)
+        optional& operator=[U](U&)
+        bool operator bool()
+        bool operator!()
+        bool operator==[U](optional&, U&)
+        bool operator!=[U](optional&, U&)
+        bool operator<[U](optional&, U&)
+        bool operator>[U](optional&, U&)
+        bool operator<=[U](optional&, U&)
+        bool operator>=[U](optional&, U&)
+
+    optional[T] make_optional[T](...) except +

python/cudf/cudf/_lib/timezone.pyx

@@ -0,0 +1,28 @@
+# Copyright (c) 2023, NVIDIA CORPORATION.
+
+from libcpp.memory cimport unique_ptr
+from libcpp.string cimport string
+from libcpp.utility cimport move
+
+from cudf._lib.cpp.io.timezone cimport (
+    make_timezone_transition_table as cpp_make_timezone_transition_table,
+)
+from cudf._lib.cpp.libcpp.optional cimport make_optional
+from cudf._lib.cpp.table.table cimport table
+from cudf._lib.utils cimport columns_from_unique_ptr
+
+
+def make_timezone_transition_table(tzdir, tzname):
+    cdef unique_ptr[table] c_result
+    cdef string c_tzdir = tzdir.encode()
+    cdef string c_tzname = tzname.encode()
+
+    with nogil:
+        c_result = move(
+            cpp_make_timezone_transition_table(
+                make_optional[string](c_tzdir),
+                c_tzname
+            )
+        )
+
+    return columns_from_unique_ptr(move(c_result))

python/cudf/cudf/core/_internals/timezones.py

@@ -0,0 +1,71 @@
+# Copyright (c) 2023, NVIDIA CORPORATION.
+
+import os
+import zoneinfo
+from functools import lru_cache
+
+from cudf._lib.timezone import build_timezone_transition_table
+from cudf.core.dataframe import DataFrame
+
+
+@lru_cache(maxsize=20)
+def get_tz_data(zone_name):
+    """
+    Return timezone data (transition times and UTC offsets) for the
+    given IANA time zone.
+
+    Parameters
+    ----------
+    zone_name: str
+        IANA time zone name
+
+    Returns
+    -------
+    DataFrame with two columns containing the transition times ("dt")
+    and corresponding UTC offsets ("offset").
+    """
+    try:
+        # like zoneinfo, we first look in TZPATH
+        return _find_and_read_tzfile_tzpath(zone_name)
+    except zoneinfo.ZoneInfoNotFoundError:
+        # if that fails, we fall back to using `tzdata`
+        return _find_and_read_tzfile_tzdata(zone_name)
+
+
+def _find_and_read_tzfile_tzpath(zone_name):
+    for search_path in zoneinfo.TZPATH:
+        if os.path.isfile(os.path.join(search_path, zone_name)):
+            return _read_tzfile_as_frame(search_path, zone_name)
+    raise zoneinfo.ZoneInfoNotFoundError(zone_name)
+
+
+def _find_and_read_tzfile_tzdata(zone_name):
+    import importlib.resources
+
+    package_base = "tzdata.zoneinfo"
+    try:
+        return _read_tzfile_as_frame(
+            str(importlib.resources.files(package_base)), zone_name
+        )
+    # TODO: make it so that the call to libcudf raises a
+    # FileNotFoundError instead of a RuntimeError
+    except (ImportError, FileNotFoundError, UnicodeEncodeError, RuntimeError):
+        # the "except" part of this try-except is basically vendored
+        # from the zoneinfo library.
+        #
+        # There are three types of exception that can be raised that all amount
+        # to "we cannot find this key":
+        #
+        # ImportError: If package_name doesn't exist (e.g. if tzdata is not
+        #   installed, or if there's an error in the folder name like
+        #   Amrica/New_York)
+        # FileNotFoundError: If resource_name doesn't exist in the package
+        #   (e.g. Europe/Krasnoy)
+        # UnicodeEncodeError: If package_name or resource_name are not UTF-8,
+        #   such as keys containing a surrogate character.
+        raise zoneinfo.ZoneInfoNotFoundError(zone_name)
+
+
+def _read_tzfile_as_frame(tzdir, zone_name):
+    dt, offsets = build_timezone_transition_table(tzdir, zone_name)
+    return DataFrame._from_columns([dt, offsets], ["dt", "offsets"])