BUG: Fix fields functions with readonly data, vaex#357

doc/source/whatsnew/v1.0.0.rst

@@ -89,7 +89,7 @@ Categorical
 Datetimelike
 ^^^^^^^^^^^^
 - Bug in :meth:`Series.__setitem__` incorrectly casting ``np.timedelta64("NaT")`` to ``np.datetime64("NaT")`` when inserting into a :class:`Series` with datetime64 dtype (:issue:`27311`)
--
+- Bug in :meth:`Series.dt` property lookups when the underlying data is read-only (:issue:`27529`)
 -
 
 

pandas/_libs/tslibs/fields.pyx

@@ -45,7 +45,7 @@ def get_time_micros(ndarray[int64_t] dtindex):
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def build_field_sarray(int64_t[:] dtindex):
+def build_field_sarray(const int64_t[:] dtindex):
     """
     Datetime as int64 representation to a structured array of fields
     """
@@ -87,7 +87,7 @@ def build_field_sarray(int64_t[:] dtindex):
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def get_date_name_field(int64_t[:] dtindex, object field, object locale=None):
+def get_date_name_field(const int64_t[:] dtindex, object field, object locale=None):
     """
     Given a int64-based datetime index, return array of strings of date
     name based on requested field (e.g. weekday_name)
@@ -137,7 +137,7 @@ def get_date_name_field(int64_t[:] dtindex, object field, object locale=None):
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def get_start_end_field(int64_t[:] dtindex, object field,
+def get_start_end_field(const int64_t[:] dtindex, object field,
                         object freqstr=None, int month_kw=12):
     """
     Given an int64-based datetime index return array of indicators
@@ -380,7 +380,7 @@ def get_start_end_field(int64_t[:] dtindex, object field,
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def get_date_field(int64_t[:] dtindex, object field):
+def get_date_field(const int64_t[:] dtindex, object field):
     """
     Given a int64-based datetime index, extract the year, month, etc.,
     field and return an array of these values.
@@ -542,7 +542,7 @@ def get_date_field(int64_t[:] dtindex, object field):
 
 @cython.wraparound(False)
 @cython.boundscheck(False)
-def get_timedelta_field(int64_t[:] tdindex, object field):
+def get_timedelta_field(const int64_t[:] tdindex, object field):
     """
     Given a int64-based timedelta index, extract the days, hrs, sec.,
     field and return an array of these values.

pandas/tests/tslibs/test_fields.py

@@ -0,0 +1,31 @@
+import numpy as np
+
+from pandas._libs.tslibs import fields
+
+import pandas.util.testing as tm
+
+
+def test_fields_readonly():
+    # https://github.com/vaexio/vaex/issues/357
+    #  fields functions should't raise when we pass read-only data
+    dtindex = np.arange(5, dtype=np.int64) * 10 ** 9 * 3600 * 24 * 32
+    dtindex.flags.writeable = False
+
+    result = fields.get_date_name_field(dtindex, "month_name")
+    expected = np.array(
+        ["January", "February", "March", "April", "May"], dtype=np.object
+    )
+    tm.assert_numpy_array_equal(result, expected)
+
+    result = fields.get_date_field(dtindex, "Y")
+    expected = np.array([1970, 1970, 1970, 1970, 1970], dtype=np.int32)
+    tm.assert_numpy_array_equal(result, expected)
+
+    result = fields.get_start_end_field(dtindex, "is_month_start", None)
+    expected = np.array([True, False, False, False, False], dtype=np.bool_)
+    tm.assert_numpy_array_equal(result, expected)
+
+    # treat dtindex as timedeltas for this next one
+    result = fields.get_timedelta_field(dtindex, "days")
+    expected = np.arange(5, dtype=np.int32) * 32
+    tm.assert_numpy_array_equal(result, expected)