date_range segfaults on None utcoffset

[frensjan]

As reported at pendulum, there are cases where creating a date_range fails with a segfault: pendulum issues 131.

Code Sample

from datetime import datetime, timedelta

from pendulum.tz.timezone import UTCTimezone
from pendulum.tz.timezone_info import UTC
import pandas as pd

tomorrow = datetime.now() + timedelta(hours=24)
now = datetime.now()

r = pd.date_range(now, tomorrow, freq='1H')

r.tz = UTC
# prints out the current date and time
print(r[0])

r.tz = UTCTimezone
# seg faults
print(r[0])

Problem description

As I understand it is allowed for tzinfo objects to return None for utcoffset according to the Python docs. However, in _get_dst_info of tslib it is assumed not to return None. As I understand from the aforementioned pendulum ticket, it is correct to return None in this case.

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.5.3.final.0 python-bits: 64 OS: Linux OS-release: 4.11.3-200.fc25.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_GB.UTF-8

pandas: 0.20.3
pytest: 3.1.3
pip: 9.0.1
setuptools: 25.1.1
Cython: None
numpy: 1.13.1
scipy: 0.19.1
xarray: None
IPython: 6.1.0
sphinx: None
patsy: None
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.6.0
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
pandas_gbq: None
pandas_datareader: None

[jreback]

duplicate issue of #15986, see discussion there.

[frensjan]

@jreback sorry, missed that one. Still think that it would be good if pandas doesn't segfault on a valid response from a timezone object (valid as in that according to the python docs a timezone object is allowed to return None).

[jreback]

@frensjan if you want to make a PR that uses a mock timezone object would be great.

Still think that it would be good if pandas doesn't segfault on a valid response from a timezone object (valid as in that according to the python docs a timezone object is allowed to return None).

I am not so sure that this library complies.