BUG: Don't raise TypeError when converting NA from string to numeric (pandas-dev#37268)

Author: dsaxton

doc/source/whatsnew/v1.2.0.rst

@@ -409,7 +409,7 @@ Conversion
 Strings
 ^^^^^^^
 - Bug in :meth:`Series.to_string`, :meth:`DataFrame.to_string`, and :meth:`DataFrame.to_latex` adding a leading space when ``index=False`` (:issue:`24980`)
--
+- Bug in :func:`to_numeric` raising a ``TypeError`` when attempting to convert a string dtype :class:`Series` containing only numeric strings and ``NA`` (:issue:`37262`)
 -
 
 

pandas/_libs/lib.pyx

@@ -2019,7 +2019,7 @@ def maybe_convert_numeric(ndarray[object] values, set na_values,
         elif util.is_bool_object(val):
             floats[i] = uints[i] = ints[i] = bools[i] = val
             seen.bool_ = True
-        elif val is None:
+        elif val is None or val is C_NA:
             seen.saw_null()
             floats[i] = complexes[i] = NaN
         elif hasattr(val, '__len__') and len(val) == 0:

pandas/tests/tools/test_to_numeric.py

@@ -707,3 +707,21 @@ def test_precision_float_conversion(strrep):
     result = to_numeric(strrep)
 
     assert result == float(strrep)
+
+
+@pytest.mark.parametrize(
+    "values, expected",
+    [
+        (["1", "2", None], Series([1, 2, np.nan])),
+        (["1", "2", "3"], Series([1, 2, 3])),
+        (["1", "2", 3], Series([1, 2, 3])),
+        (["1", "2", 3.5], Series([1, 2, 3.5])),
+        (["1", None, 3.5], Series([1, np.nan, 3.5])),
+        (["1", "2", "3.5"], Series([1, 2, 3.5])),
+    ],
+)
+def test_to_numeric_from_nullable_string(values, expected):
+    # https://github.com/pandas-dev/pandas/issues/37262
+    s = Series(values, dtype="string")
+    result = to_numeric(s)
+    tm.assert_series_equal(result, expected)