From 28a242d932679e86b4c1bd7607e4958ab9f09aae Mon Sep 17 00:00:00 2001
From: Matthew Zeitlin <37011898+mzeitlin11@users.noreply.github.com>
Date: Tue, 23 Mar 2021 11:17:56 -0400
Subject: [PATCH] Backport PR #40525: BUG: to_json failing on PyPy

---
 doc/source/whatsnew/v1.2.4.rst            |  1 +
 pandas/_libs/src/ujson/python/objToJSON.c | 23 +++++++++++------------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/doc/source/whatsnew/v1.2.4.rst b/doc/source/whatsnew/v1.2.4.rst
index edf23bf89d7e1..c7bc337239faf 100644
--- a/doc/source/whatsnew/v1.2.4.rst
+++ b/doc/source/whatsnew/v1.2.4.rst
@@ -16,6 +16,7 @@ Fixed regressions
 ~~~~~~~~~~~~~~~~~
 
 - Fixed regression in :meth:`DataFrame.sum` when ``min_count`` greater than the :class:`DataFrame` shape was passed resulted in a ``ValueError`` (:issue:`39738`)
+- Fixed regression in :meth:`DataFrame.to_json` raising ``AttributeError`` when run on PyPy (:issue:`39837`)
 -
 
 .. ---------------------------------------------------------------------------
diff --git a/pandas/_libs/src/ujson/python/objToJSON.c b/pandas/_libs/src/ujson/python/objToJSON.c
index 59298522d86d1..5a3cccdbfea7e 100644
--- a/pandas/_libs/src/ujson/python/objToJSON.c
+++ b/pandas/_libs/src/ujson/python/objToJSON.c
@@ -272,18 +272,6 @@ static PyObject *get_sub_attr(PyObject *obj, char *attr, char *subAttr) {
     return ret;
 }
 
-static int is_simple_frame(PyObject *obj) {
-    PyObject *check = get_sub_attr(obj, "_mgr", "is_mixed_type");
-    int ret = (check == Py_False);
-
-    if (!check) {
-        return 0;
-    }
-
-    Py_DECREF(check);
-    return ret;
-}
-
 static Py_ssize_t get_attr_length(PyObject *obj, char *attr) {
     PyObject *tmp = PyObject_GetAttrString(obj, attr);
     Py_ssize_t ret;
@@ -301,6 +289,17 @@ static Py_ssize_t get_attr_length(PyObject *obj, char *attr) {
     return ret;
 }
 
+static int is_simple_frame(PyObject *obj) {
+    PyObject *mgr = PyObject_GetAttrString(obj, "_mgr");
+    if (!mgr) {
+        return 0;
+    }
+    int ret = (get_attr_length(mgr, "blocks") <= 1);
+
+    Py_DECREF(mgr);
+    return ret;
+}
+
 static npy_int64 get_long_attr(PyObject *o, const char *attr) {
     npy_int64 long_val;
     PyObject *value = PyObject_GetAttrString(o, attr);