PERF: slow tests

pandas/core/arrays/datetimelike.py

@@ -35,6 +35,7 @@
     Timestamp,
     delta_to_nanoseconds,
     iNaT,
+    ints_to_pydatetime,
     to_offset,
 )
 from pandas._libs.tslibs.fields import (
@@ -406,6 +407,19 @@ def astype(self, dtype, copy: bool = True):
         dtype = pandas_dtype(dtype)
 
         if is_object_dtype(dtype):
+            if self.dtype.kind == "M":
+                # *much* faster than self._box_values
+                #  for e.g. test_get_loc_tuple_monotonic_above_size_cutoff
+                i8data = self.asi8.ravel()
+                converted = ints_to_pydatetime(
+                    i8data,
+                    # error: "DatetimeLikeArrayMixin" has no attribute "tz"
+                    tz=self.tz,  # type: ignore[attr-defined]
+                    freq=self.freq,
+                    box="timestamp",
+                )
+                return converted.reshape(self.shape)
+
             return self._box_values(self.asi8.ravel()).reshape(self.shape)
 
         elif isinstance(dtype, ExtensionDtype):

pandas/core/dtypes/common.py

@@ -528,6 +528,15 @@ def is_categorical_dtype(arr_or_dtype) -> bool:
     return CategoricalDtype.is_dtype(arr_or_dtype)
 
 
+def is_string_or_object_np_dtype(dtype: np.dtype) -> bool:
+    """
+    Faster alternative to is_string_dtype, assumes we have a np.dtype object.
+    """
+    # error: Non-overlapping equality check (left operand type: "dtype[Any]",
+    # right operand type: "Type[object]")
+    return dtype == object or dtype.kind in "SU"  # type: ignore[comparison-overlap]
+
+
 def is_string_dtype(arr_or_dtype) -> bool:
     """
     Check whether the provided array or dtype is of the string dtype.

pandas/core/dtypes/missing.py

@@ -33,7 +33,7 @@
     is_integer_dtype,
     is_object_dtype,
     is_scalar,
-    is_string_dtype,
+    is_string_or_object_np_dtype,
     needs_i8_conversion,
 )
 from pandas.core.dtypes.dtypes import (
@@ -242,7 +242,7 @@ def _isna_array(values: ArrayLike, inf_as_na: bool = False):
             result = libmissing.isnaobj(values.to_numpy(), inf_as_na=inf_as_na)
         else:
             result = values.isna()
-    elif is_string_dtype(dtype):
+    elif is_string_or_object_np_dtype(values.dtype):
         result = _isna_string_dtype(values, inf_as_na=inf_as_na)
     elif needs_i8_conversion(dtype):
         # this is the NaT pattern
@@ -376,7 +376,10 @@ def isna_compat(arr, fill_value=np.nan) -> bool:
 
 
 def array_equivalent(
-    left, right, strict_nan: bool = False, dtype_equal: bool = False
+    left,
+    right,
+    strict_nan: bool = False,
+    dtype_equal: bool = False,
 ) -> bool:
     """
     True if two arrays, left and right, have equal non-NaN elements, and NaNs
@@ -421,13 +424,13 @@ def array_equivalent(
 
     if dtype_equal:
         # fastpath when we require that the dtypes match (Block.equals)
-        if is_float_dtype(left.dtype) or is_complex_dtype(left.dtype):
+        if left.dtype.kind in ["f", "c"]:
             return _array_equivalent_float(left, right)
         elif is_datetimelike_v_numeric(left.dtype, right.dtype):
             return False
         elif needs_i8_conversion(left.dtype):
             return _array_equivalent_datetimelike(left, right)
-        elif is_string_dtype(left.dtype):
+        elif is_string_or_object_np_dtype(left.dtype):
             # TODO: fastpath for pandas' StringDtype
             return _array_equivalent_object(left, right, strict_nan)
         else:

pandas/tests/dtypes/test_common.py

@@ -154,6 +154,7 @@ def get_is_dtype_funcs():
 
     """
     fnames = [f for f in dir(com) if (f.startswith("is_") and f.endswith("dtype"))]
+    fnames.remove("is_string_or_object_np_dtype")  # fastpath requires np.dtype obj
     return [getattr(com, fname) for fname in fnames]
 
 

pandas/tests/indexing/test_chaining_and_caching.py

@@ -20,14 +20,12 @@
 
 
 def random_text(nobs=100):
-    df = []
-    for i in range(nobs):
-        idx = np.random.randint(len(letters), size=2)
-        idx.sort()
+    # Construct a DataFrame where each row is a random slice from 'letters'
+    idxs = np.random.randint(len(letters), size=(nobs, 2))
+    idxs.sort(axis=1)
+    strings = [letters[x[0] : x[1]] for x in idxs]
 
-        df.append([letters[idx[0] : idx[1]]])
-
-    return DataFrame(df, columns=["letters"])
+    return DataFrame(strings, columns=["letters"])
 
 
 class TestCaching: