Backport PR #31524: BUG: non-iterable value in meta raise error in json_normalize (#32629)

Co-authored-by: Kaiqi Dong <kaiqi@kth.se>

Author: meeseeksmachine

doc/source/whatsnew/v1.0.2.rst

@@ -78,6 +78,7 @@ Bug fixes
 **I/O**
 
 - Using ``pd.NA`` with :meth:`DataFrame.to_json` now correctly outputs a null value instead of an empty object (:issue:`31615`)
+- Bug in :meth:`pandas.json_normalize` when value in meta path is not iterable (:issue:`31507`)
 - Fixed pickling of ``pandas.NA``. Previously a new object was returned, which broke computations relying on ``NA`` being a singleton (:issue:`31847`)
 - Fixed bug in parquet roundtrip with nullable unsigned integer dtypes (:issue:`31896`).
 

pandas/io/json/_normalize.py

@@ -8,6 +8,7 @@
 import numpy as np
 
 from pandas._libs.writers import convert_json_to_lines
+from pandas._typing import Scalar
 from pandas.util._decorators import deprecate
 
 import pandas as pd
@@ -230,14 +231,28 @@ def _json_normalize(
     Returns normalized data with columns prefixed with the given string.
     """
 
-    def _pull_field(js: Dict[str, Any], spec: Union[List, str]) -> Iterable:
+    def _pull_field(
+        js: Dict[str, Any], spec: Union[List, str]
+    ) -> Union[Scalar, Iterable]:
+        """Internal function to pull field"""
         result = js  # type: ignore
         if isinstance(spec, list):
             for field in spec:
                 result = result[field]
         else:
             result = result[spec]
+        return result
+
+    def _pull_records(js: Dict[str, Any], spec: Union[List, str]) -> Iterable:
+        """
+        Interal function to pull field for records, and similar to
+        _pull_field, but require to return Iterable. And will raise error
+        if has non iterable value.
+        """
+        result = _pull_field(js, spec)
 
+        # GH 31507 GH 30145, if result is not Iterable, raise TypeError if not
+        # null, otherwise return an empty list
         if not isinstance(result, Iterable):
             if pd.isnull(result):
                 result = []  # type: ignore
@@ -246,7 +261,6 @@ def _pull_field(js: Dict[str, Any], spec: Union[List, str]) -> Iterable:
                     f"{js} has non iterable value {result} for path {spec}. "
                     "Must be iterable or null."
                 )
-
         return result
 
     if isinstance(data, list) and not data:
@@ -296,7 +310,7 @@ def _recursive_extract(data, path, seen_meta, level=0):
                 _recursive_extract(obj[path[0]], path[1:], seen_meta, level=level + 1)
         else:
             for obj in data:
-                recs = _pull_field(obj, path[0])
+                recs = _pull_records(obj, path[0])
                 recs = [
                     nested_to_record(r, sep=sep, max_level=max_level)
                     if isinstance(r, dict)

pandas/tests/io/json/test_normalize.py

@@ -486,6 +486,16 @@ def test_non_interable_record_path_errors(self):
         with pytest.raises(TypeError, match=msg):
             json_normalize([test_input], record_path=[test_path])
 
+    def test_meta_non_iterable(self):
+        # GH 31507
+        data = """[{"id": 99, "data": [{"one": 1, "two": 2}]}]"""
+
+        result = json_normalize(json.loads(data), record_path=["data"], meta=["id"])
+        expected = DataFrame(
+            {"one": [1], "two": [2], "id": np.array([99], dtype=object)}
+        )
+        tm.assert_frame_equal(result, expected)
+
 
 class TestNestedToRecord:
     def test_flat_stays_flat(self):