From 5bdd8a411ba5417e523bcd7086ea01c9d1b0cf72 Mon Sep 17 00:00:00 2001
From: Sumanau Sareen <sumanau.sareen@healthifyme.com>
Date: Mon, 20 May 2019 12:26:33 +0530
Subject: [PATCH 1/3] Add defensive check for argument `errors` in func
 `to_numeric`.

---
 pandas/core/tools/numeric.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/pandas/core/tools/numeric.py b/pandas/core/tools/numeric.py
index 08ce649d8602c..d7a1b1119ce4b 100644
--- a/pandas/core/tools/numeric.py
+++ b/pandas/core/tools/numeric.py
@@ -105,6 +105,9 @@ def to_numeric(arg, errors='raise', downcast=None):
     if downcast not in (None, 'integer', 'signed', 'unsigned', 'float'):
         raise ValueError('invalid downcasting method provided')
 
+    if errors not in ('ignore', 'raise', 'coerce'):
+        raise ValueError('invalid error value specified')
+
     is_series = False
     is_index = False
     is_scalars = False

From 8d96ef8b267740958f88c506f5d0d4ac978708e5 Mon Sep 17 00:00:00 2001
From: Sumanau Sareen <sumanau.sareen@healthifyme.com>
Date: Mon, 20 May 2019 13:40:24 +0530
Subject: [PATCH 2/3] Added test for validating if right error message is
 raised.

---
 pandas/tests/tools/test_numeric.py | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/pandas/tests/tools/test_numeric.py b/pandas/tests/tools/test_numeric.py
index 5d3903cb93bd5..6e3e768f9360f 100644
--- a/pandas/tests/tools/test_numeric.py
+++ b/pandas/tests/tools/test_numeric.py
@@ -413,6 +413,16 @@ def test_downcast_invalid_cast():
         to_numeric(data, downcast=invalid_downcast)
 
 
+def test_errors_invalid_value():
+    # see gh-26466
+    data = ["1", 2, 3]
+    invalid_error_value = "invalid"
+    msg = "invalid error value specified"
+
+    with pytest.raises(ValueError, match=msg):
+        to_numeric(data, errors=invalid_error_value)
+
+
 @pytest.mark.parametrize("data", [
     ["1", 2, 3],
     [1, 2, 3],

From 4de3f1a0c5a4c341c63e6c49835b2e6e77494ea5 Mon Sep 17 00:00:00 2001
From: Sumanau Sareen <sumanau.sareen@healthifyme.com>
Date: Mon, 20 May 2019 15:18:01 +0530
Subject: [PATCH 3/3] Added change details, in v.0.25.0.rst file.

---
 doc/source/whatsnew/v0.25.0.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/source/whatsnew/v0.25.0.rst b/doc/source/whatsnew/v0.25.0.rst
index b2d1aa299a45a..9e04dcaa41416 100644
--- a/doc/source/whatsnew/v0.25.0.rst
+++ b/doc/source/whatsnew/v0.25.0.rst
@@ -41,6 +41,7 @@ Other Enhancements
 - :meth:`DataFrame.query` and :meth:`DataFrame.eval` now supports quoting column names with backticks to refer to names with spaces (:issue:`6508`)
 - :func:`merge_asof` now gives a more clear error message when merge keys are categoricals that are not equal (:issue:`26136`)
 - :meth:`pandas.core.window.Rolling` supports exponential (or Poisson) window type (:issue:`21303`)
+- :func:`to_numeric` now gives a error message when errors argument value is not in the tuple of accepted values. (:issue:`26466`)
 
 .. _whatsnew_0250.api_breaking: