apply() silently removes time zone information from DateTime values

[adamdivak]

Hi,

apply() silently removes time zone information from DateTime values. I think this bug is related to #10668, but it is apparently not the same.

Code Sample, a copy-pastable example if possible

import pandas as pd
date_range = pd.date_range('1/1/2011', periods=5, freq='H')
date_range = date_range.tz_localize('Europe/Budapest')
s = pd.Series(date_range, index=date_range)
s

2011-01-01 00:00:00+01:00   2011-01-01 00:00:00+01:00
2011-01-01 01:00:00+01:00   2011-01-01 01:00:00+01:00
2011-01-01 02:00:00+01:00   2011-01-01 02:00:00+01:00
2011-01-01 03:00:00+01:00   2011-01-01 03:00:00+01:00
2011-01-01 04:00:00+01:00   2011-01-01 04:00:00+01:00
Freq: H, dtype: datetime64[ns, Europe/Budapest]

Create a simple apply function which does nothing but returns each value. Notice that that values are converted to UTC by default and the timezone information is lost, and a timezone-naive value is returned instead.

def apply_function(dt):
    return dt
s.apply(apply_function)

2011-01-01 00:00:00+01:00   2010-12-31 23:00:00
2011-01-01 01:00:00+01:00   2011-01-01 00:00:00
2011-01-01 02:00:00+01:00   2011-01-01 01:00:00
2011-01-01 03:00:00+01:00   2011-01-01 02:00:00
2011-01-01 04:00:00+01:00   2011-01-01 03:00:00
Freq: H, dtype: datetime64[ns]

Expected Output

Apply is expected to return the original series, values unchanged, including the time zone information.

output of pd.show_versions()

INSTALLED VERSIONS
------------------
commit: None
python: 3.4.4.final.0
python-bits: 64
OS: Linux
OS-release: 4.2.0-27-generic
machine: x86_64
processor: 
byteorder: little
LC_ALL: en_US.UTF-8
LANG: en_US.UTF-8

pandas: 0.17.1
nose: None
pip: 8.0.2
setuptools: 20.1.1
Cython: 0.23.4
numpy: 1.10.4
scipy: 0.17.0
statsmodels: 0.6.1
IPython: 4.1.1
sphinx: None
patsy: 0.4.0
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: None
tables: None
numexpr: None
matplotlib: 1.5.1
openpyxl: None
xlrd: 0.9.4
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
Jinja2: None

[rockg]

I believe this is the same as #11757 which I have neglected to finish. It was turning out to be trickier than I had hoped.

[jreback]

I agree. @yosuah thanks for the report.