ENH: Add the decimal.Decimal type to infer_dtypes (pandas-dev#15690)

Author: margaret

pandas/_libs/src/inference.pyx

@@ -308,7 +308,6 @@ def infer_dtype(object value):
     'categorical'
 
     """
-
     cdef:
         Py_ssize_t i, n
         object val
@@ -407,6 +406,9 @@ def infer_dtype(object value):
         if is_time_array(values):
             return 'time'
 
+    elif is_decimal(val):
+        return 'decimal'
+
     elif util.is_float_object(val):
         if is_float_array(values):
             return 'floating'

pandas/tests/dtypes/test_inference.py

@@ -9,6 +9,7 @@
 import collections
 import re
 from datetime import datetime, date, timedelta, time
+from decimal import Decimal
 import numpy as np
 import pytz
 import pytest
@@ -462,6 +463,11 @@ def test_floats(self):
         result = lib.infer_dtype(arr)
         assert result == 'floating'
 
+    def test_decimals(self):
+        arr = np.array([Decimal(1), Decimal(2), Decimal(3)])
+        result = lib.infer_dtype(arr)
+        assert result == 'decimal'
+
     def test_string(self):
         pass