Fix #22903 for lib.is_scalar missing PEP 3141 numbers

Author: tm9k1

doc/source/whatsnew/v0.24.0.txt

@@ -239,6 +239,7 @@ For situations where you need an ``ndarray`` of ``Interval`` objects, use
    np.asarray(idx)
    idx.values.astype(object)
 
+
 .. _whatsnew_0240.api.timezone_offset_parsing:
 
 Parsing Datetime Strings with Timezone Offsets
@@ -900,3 +901,5 @@ Other
 - :meth:`DataFrame.nlargest` and :meth:`DataFrame.nsmallest` now returns the correct n values when keep != 'all' also when tied on the first columns (:issue:`22752`)
 - :meth:`~pandas.io.formats.style.Styler.bar` now also supports tablewise application (in addition to rowwise and columnwise) with ``axis=None`` and setting clipping range with ``vmin`` and ``vmax`` (:issue:`21548` and :issue:`21526`). ``NaN`` values are also handled properly.
 - Logical operations ``&, |, ^`` between :class:`Series` and :class:`Index` will no longer raise ``ValueError`` (:issue:`22092`)
+- Checking PEP 3141 numbers in :func:`~pandas.api.types.is_scalar` function returns ``True`` (:issue:`22903`)
+- 

pandas/_libs/lib.pyx

@@ -1,5 +1,8 @@
 # -*- coding: utf-8 -*-
 from decimal import Decimal
+from fractions import Fraction
+from numbers import Number
+
 import sys
 
 import cython
@@ -15,7 +18,6 @@ from cpython.datetime cimport (PyDateTime_Check, PyDate_Check,
                                PyDateTime_IMPORT)
 PyDateTime_IMPORT
 
-
 import numpy as np
 cimport numpy as cnp
 from numpy cimport (ndarray, PyArray_NDIM, PyArray_GETITEM,
@@ -107,7 +109,10 @@ def memory_usage_of_objects(arr: object[:]) -> int64_t:
 def is_scalar(val: object) -> bint:
     """
     Return True if given value is scalar.
-
+    
+    Parameters
+    ----------
+    val : input argument of any type
     This includes:
     - numpy array scalar (e.g. np.int64)
     - Python builtin numerics
@@ -119,12 +124,42 @@ def is_scalar(val: object) -> bint:
     - instances of decimal.Decimal
     - Interval
     - DateOffset
+    - Fraction
+    - Number
 
+    Returns
+    -------
+    True if the given value is scalar, False otherwise.
+    
+    Examples
+    --------
+    >>> dt = pd.datetime.datetime(2018, 10, 3)
+    >>> pd.is_scalar(dt)
+    True
+
+    >>> pd.api.types.is_scalar([2, 3])
+    False
+    
+    >>> pd.api.types.is_scalar({0:1, 2:3})
+    False
+    
+    >>> pd.api.types.is_scalar((0, 2))
+    False
+    
+    pandas supports PEP 3141 numbers:
+    
+    >>> from fractions import Fraction
+    >>> pd.api.types.is_scalar(Fraction(3, 5))
+    True
+
+    >>> from numbers import Number
+    >>> pd.api.types.is_scalar(Number())
+    True
     """
 
     return (cnp.PyArray_IsAnyScalar(val)
             # As of numpy-1.9, PyArray_IsAnyScalar misses bytearrays on Py3.
-            or isinstance(val, bytes)
+            or isinstance(val,(bytes, Fraction, Number))
             # We differ from numpy (as of 1.10), which claims that None is
             # not scalar in np.isscalar().
             or val is None
@@ -136,7 +171,6 @@ def is_scalar(val: object) -> bint:
             or is_interval(val)
             or util.is_offset_object(val))
 
-
 def item_from_zerodim(val: object) -> object:
     """
     If the value is a zerodim array, return the item it contains.

pandas/tests/dtypes/test_inference.py

@@ -10,10 +10,11 @@
 import re
 from datetime import datetime, date, timedelta, time
 from decimal import Decimal
+from numbers import Number
+from fractions import Fraction
 import numpy as np
 import pytz
 import pytest
-
 import pandas as pd
 from pandas._libs import tslib, lib, missing as libmissing
 from pandas import (Series, Index, DataFrame, Timedelta,
@@ -1120,6 +1121,8 @@ def test_is_scalar_builtin_scalars(self):
         assert is_scalar(None)
         assert is_scalar(True)
         assert is_scalar(False)
+        assert is_scalar(Number())
+        assert is_scalar(Fraction())
         assert is_scalar(0.)
         assert is_scalar(np.nan)
         assert is_scalar('foobar')
@@ -1184,7 +1187,6 @@ def test_is_scalar_pandas_containers(self):
         assert not is_scalar(Index([]))
         assert not is_scalar(Index([1]))
 
-
 def test_datetimeindex_from_empty_datetime64_array():
     for unit in ['ms', 'us', 'ns']:
         idx = DatetimeIndex(np.array([], dtype='datetime64[%s]' % unit))