COMPAT: support Timestamp.timestamp() in py2.x

[femtotrader]

Code Sample, a copy-pastable example if possible

Python 3

In [3]: pd.Timestamp('1970-01-01', tz='UTC').timestamp()
Out[3]: 0.0

Python 2.7

In [4]: pd.Timestamp('1970-01-01', tz='UTC').timestamp()

raises

AttributeError: 'Timestamp' object has no attribute 'timestamp'

Problem description

Consistency between same Pandas version (despite difference with Python version)

Expected Output

Same output for Python 2.x and Python 3 (what ever timezone is, or without timezone)

Output of pd.show_versions()

Python 3.x

INSTALLED VERSIONS

commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Darwin
OS-release: 16.7.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: fr_FR.UTF-8
LOCALE: fr_FR.UTF-8

pandas: 0.20.1
pytest: 3.1.2
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
xarray: 0.9.5
IPython: 5.3.0
sphinx: 1.5.6
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.3.0
numexpr: 2.6.2
feather: None
matplotlib: 2.0.2
openpyxl: 2.4.7
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.3
bs4: 4.6.0
html5lib: 0.999
sqlalchemy: 1.1.9
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: 0.5.0

Python 2.7 (install using conda virtual env)

In [21]: pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 2.7.13.final.0
python-bits: 64
OS: Darwin
OS-release: 16.7.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: fr_FR.UTF-8
LOCALE: None.None

pandas: 0.20.3
pytest: None
pip: 9.0.1
setuptools: 27.2.0
Cython: None
numpy: 1.13.1
scipy: None
xarray: None
IPython: 5.3.0
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: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
pandas_gbq: None
pandas_datareader: None

Related to: pydata/pandas-datareader#378 (comment)

SO question: https://stackoverflow.com/questions/40473442/attributeerror-timestamp-object-has-no-attribute-timestamp

[gfyoung]

@femtotrader : Thanks for reporting this! Indeed, this traces back to the fact that Timestamp inherits timestamp from datetime.datetime in Python 3.x, but that is not the case in Python 2.7.

Unless implementing .timestamp is easy to do, I'm not sure how we could best address this given that the incompatibility stems for a core Python library.

[chris-b1]

I suppose we could shim this in, implementation something like this

In [116]: ts = pd.Timestamp('2014-10-11 11:00:01.12345678', tz='US/Central')

In [117]: ts.timestamp()
Out[117]: 1413043201.123456

In [118]: ts.value // 1000 / 1000000  # truncate to ms, divide to s
Out[118]: 1413043201.123456

[femtotrader]

Thanks @chris-b1
For Python 2.7 it should be ts.value // 1000 / 1000000.0 because ts.value // 1000 / 1000000 returns an integer

[jreback]

this would be ok.

[femtotrader]

When Timestamp haven't timezone we should add an offset
See pydata/pandas-datareader#378 (comment)

[jbrockmendel]

Went to go implement this and now I'm confused (might relate to confusion regarding #17734). Why does an offset need to be added? I thought ts.value is already "in" UTC.