Repository: pandas-dev/pandas

Issue:
BUG: Setting Timestamp with timezone with .at raises TypeError
#### Code Sample, a copy-pastable example if possible

```python
import pytz 
import pandas 

series = pd.Series(pd.Timestamp('2017-08-05 00:00:00+0100', tz=pytz.FixedOffset(60)))
series.at[1] = pd.Timestamp('2017-08-05 00:00:00+0100', tz=pytz.FixedOffset(60))

# this produces 
TypeError: Argument 'arr' has incorrect type (expected numpy.ndarray, got DatetimeArray)
```
#### Problem description
I would expect to be able to operate on a series of timestamps

#### Expected Output

no error 


#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.7.final.0
python-bits: 64
OS: Linux
OS-release: 4.15.0-45-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.4
pytest: 4.1.1
pip: 18.1
setuptools: 40.6.3
Cython: None
numpy: 1.16.0
scipy: 1.2.0
pyarrow: None
xarray: 0.11.3
IPython: 7.2.0
sphinx: None
patsy: None
dateutil: 2.7.5
pytz: 2018.9
blosc: None
bottleneck: None
tables: 3.4.4
numexpr: 2.6.9
feather: None
matplotlib: 3.0.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: 1.2.16
pymysql: None
psycopg2: 2.7.6.1 (dt dec pq3 ext lo64)
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: 0.9.0
pandas_datareader: None
</details>



Discussion:
Note `loc` still works

```
In [13]: import pytz
    ...: import pandas
    ...:
    ...: series = pd.Series(pd.Timestamp('2017-08-05 00:00:00+0100', tz=pytz.FixedOffset(60)))
    ...: series.loc[1] = pd.Timestamp('2017-08-05 00:00:00+0100', tz=pytz.FixedOffset(60))

In [14]: series
Out[14]:
0   2017-08-05 00:00:00+01:00
1   2017-08-05 00:00:00+01:00
dtype: datetime64[ns, pytz.FixedOffset(60)]
```

Guessing since switching to ExtensionArrays under the hood `at` was overlooked. PRs welcome!

Resolving patch:
diff --git a/pandas/core/series.py b/pandas/core/series.py
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -1229,7 +1229,7 @@ def _set_value(self, label, value, takeable=False):
                 self._values[label] = value
             else:
                 self.index._engine.set_value(self._values, label, value)
-        except KeyError:
+        except (KeyError, TypeError):
 
             # set using a non-recursive method
             self.loc[label] = value


Test patch:
diff --git a/pandas/tests/indexing/test_scalar.py b/pandas/tests/indexing/test_scalar.py
--- a/pandas/tests/indexing/test_scalar.py
+++ b/pandas/tests/indexing/test_scalar.py
@@ -185,6 +185,14 @@ def test_at_with_tz(self):
         result = df.at[0, 'date']
         assert result == expected
 
+    def test_series_set_tz_timestamp(self, tz_naive_fixture):
+        # GH 25506
+        ts = Timestamp('2017-08-05 00:00:00+0100', tz=tz_naive_fixture)
+        result = Series(ts)
+        result.at[1] = ts
+        expected = Series([ts, ts])
+        tm.assert_series_equal(result, expected)
+
     def test_mixed_index_at_iat_loc_iloc_series(self):
         # GH 19860
         s = Series([1, 2, 3, 4, 5], index=['a', 'b', 'c', 1, 2])