ENH: Added errors{'raise','ignore'} for keys not found in meta for js…

…on_normalize

Author: dickreuter <dickreuter@yahoo.com>

Closes pandas-dev#14583 from dickreuter/json_normalize_enhancement and squashes the following commits:

701c140 [dickreuter] adjusted formatting
3c94206 [dickreuter] shortened lines to pass linting
2028924 [dickreuter] doc changes
d298588 [dickreuter] Fixed as instructed in pull request page
bcfbf18 [dickreuter] Avoids exception when pandas.io.json.json_normalize

doc/source/whatsnew/v0.20.0.txt

@@ -61,6 +61,8 @@ Other enhancements
 - The ``usecols`` argument in ``pd.read_csv`` now accepts a callable function as a value  (:issue:`14154`)
 - ``pd.DataFrame.plot`` now prints a title above each subplot if ``suplots=True`` and ``title`` is a list of strings (:issue:`14753`)
 - ``pd.Series.interpolate`` now supports timedelta as an index type with ``method='time'`` (:issue:`6424`)
+- ``pandas.io.json.json_normalize()`` gained the option ``errors='ignore'|'raise'``; the default is ``errors='raise'`` which is backward compatible. (:issue:`14583`)
+
 
 .. _whatsnew_0200.api_breaking:
 

pandas/io/json.py

@@ -725,7 +725,9 @@ def nested_to_record(ds, prefix="", level=0):
 
 def json_normalize(data, record_path=None, meta=None,
                    meta_prefix=None,
-                   record_prefix=None):
+                   record_prefix=None,
+                   errors='raise'):
+
     """
     "Normalize" semi-structured JSON data into a flat table
 
@@ -742,6 +744,13 @@ def json_normalize(data, record_path=None, meta=None,
         If True, prefix records with dotted (?) path, e.g. foo.bar.field if
         path to records is ['foo', 'bar']
     meta_prefix : string, default None
+    errors : {'raise', 'ignore'}, default 'raise'
+        * ignore : will ignore KeyError if keys listed in meta are not
+        always present
+        * raise : will raise KeyError if keys listed in meta are not
+        always present
+
+        .. versionadded:: 0.20.0
 
     Returns
     -------
@@ -841,7 +850,16 @@ def _recursive_extract(data, path, seen_meta, level=0):
                     if level + 1 > len(val):
                         meta_val = seen_meta[key]
                     else:
-                        meta_val = _pull_field(obj, val[level:])
+                        try:
+                            meta_val = _pull_field(obj, val[level:])
+                        except KeyError as e:
+                            if errors == 'ignore':
+                                meta_val = np.nan
+                            else:
+                                raise \
+                                    KeyError("Try running with "
+                                             "errors='ignore' as key "
+                                             "%s is not always present", e)
                     meta_vals[key].append(meta_val)
 
                 records.extend(recs)

pandas/io/tests/json/test_json_norm.py

@@ -225,6 +225,65 @@ def test_nested_flattens(self):
 
         self.assertEqual(result, expected)
 
+    def test_json_normalize_errors(self):
+        # GH14583: If meta keys are not always present
+        # a new option to set errors='ignore' has been implemented
+        i = {
+            "Trades": [{
+                "general": {
+                    "tradeid": 100,
+                    "trade_version": 1,
+                    "stocks": [{
+
+                        "symbol": "AAPL",
+                        "name": "Apple",
+                        "price": "0"
+                    }, {
+                        "symbol": "GOOG",
+                        "name": "Google",
+                        "price": "0"
+                    }
+                    ]
+                }
+            }, {
+                "general": {
+                    "tradeid": 100,
+                    "stocks": [{
+                        "symbol": "AAPL",
+                        "name": "Apple",
+                        "price": "0"
+                    }, {
+                        "symbol": "GOOG",
+                        "name": "Google",
+                        "price": "0"
+                    }
+                    ]
+                }
+            }
+            ]
+        }
+        j = json_normalize(data=i['Trades'],
+                           record_path=[['general', 'stocks']],
+                           meta=[['general', 'tradeid'],
+                                 ['general', 'trade_version']],
+                           errors='ignore')
+        expected = {'general.trade_version': {0: 1.0, 1: 1.0, 2: '', 3: ''},
+                    'general.tradeid': {0: 100, 1: 100, 2: 100, 3: 100},
+                    'name': {0: 'Apple', 1: 'Google', 2: 'Apple', 3: 'Google'},
+                    'price': {0: '0', 1: '0', 2: '0', 3: '0'},
+                    'symbol': {0: 'AAPL', 1: 'GOOG', 2: 'AAPL', 3: 'GOOG'}}
+
+        self.assertEqual(j.fillna('').to_dict(), expected)
+
+        self.assertRaises(KeyError,
+                          json_normalize, data=i['Trades'],
+                          record_path=[['general', 'stocks']],
+                          meta=[['general', 'tradeid'],
+                                ['general', 'trade_version']],
+                          errors='raise'
+                          )
+
+
 if __name__ == '__main__':
     nose.runmodule(argv=[__file__, '-vvs', '-x', '--pdb',
                          '--pdb-failure', '-s'], exit=False)