sact.epoch¶

sact.epoch is a Python library using Zope Component Architecture providing legacy datetime.datetime subclass that allows a simple time abstraction mecanism, allowing code that would use it as reference to be diverted both on the local time zone and the real time.

FEATURES¶

using sact.epoch.Time:

you’ll never again hear about “naive” time, a Time instance represents one absolute unique moment, even if you can look at these moments through different timezones.
you will be able to get timestamp of any Time object without thinking about it (that was rather complicated with datetime, see: http://stackoverflow.com/questions/5067218/get-utc-timestamp-in-python-with-datetime, and eventually made it in python 3.3, without clearing all the complexity of naive datetimes... http://docs.python.org/3/library/datetime.html#datetime.datetime.timestamp,)
you’ll be able to test code that make use of .now() by setting or stopping current time as seen be .now() function without touching at the code. Even more, you’ll be able to divert local timezone access easily.

These assumptions are in the code:

Timestamps are UTC. Time object are instanced UTC by default when not specified otherwise, so .fromtimestamp and .utcfromtimestamp does the same thing in sact.epoch.Time.
Time object are considered equal if their timestamp is equal. Note that 2 Time instance could be on different timezone and be considered equal.
Time object is nothing more than an absolute time reference (a timestamp), and a timezone information.
Access to system information, for instance: call to get the local system timezone, and call to get the local system time, should be explicit or changeable for tests. (legacy module time and datetime will make lot of these calls)

Replaces datetime¶

You can replace datetime by Time... it has the same API. So you could instanciate them as you instanciated ``datetime``s:

>>> from sact.epoch import Time
>>> Time.now()  
<Time ...+00:00>
>>> Time(1980, 1, 1)
<Time 1980-01-01 00:00:00+00:00>

With a difference: there are no naive Time, this means that all Time objects have a timezone set. By default, it’s UTC timezone that is used.

You could also use a valid datetime to instanciate a Time object:

>>> from sact.epoch.clock import Time, UTC, TzLocal
>>> from datetime import datetime
>>> d = datetime(1970, 1, 1, tzinfo=UTC())
>>> Time(d)
<Time 1970-01-01 00:00:00+00:00>

Or use strptime(), notice that we need a new hint_src_tz param, which informs the code in which timezone the parsed string should be considered:

>>> Time.strptime('2000-01-01', '%Y-%m-%d', hint_src_tz=UTC())
<Time 2000-01-01 00:00:00+00:00>

Manageable clock for tests¶

There are code that deals with the current system time and timezone. sact.epoch will give you mean to divert these calls so as to fix time and timezone so that test output remain checkable.

Diverting system clock¶

This use zope utilities. We can give a better view thanks to a manageable clock as time reference:

>>> from sact.epoch.clock import ManageableClock
>>> clock = ManageableClock()

We will stop the time to epoch:

>>> clock.stop()
>>> clock.ts = 0

And register our clock as the General clock:

>>> from zope.component import globalSiteManager as gsm
>>> gsm.registerUtility(clock)

>>> Time.now()
<Time 1970-01-01 00:00:00+00:00>

Diverting system timezone¶

Now, let’s set our TzTest as local timezone, remember it has 5 minutes difference to UTC:

>>> from sact.epoch import testTimeZone
>>> from sact.epoch.interfaces import ITimeZone

>>> gsm.registerUtility(testTimeZone, ITimeZone, name='local')

Testing¶

We are now ready to test code:

>>> Time.now()
<Time 1970-01-01 00:00:00+00:00>

>>> Time.now().local
<Time 1970-01-01 00:05:00+00:05>

As you can see, time has frozen, local time is detected as being our strange testTimeZone which is 5 minute ahead.

Remember that in the following tests, local time zone will be the testTimeZone, and the clock is set to EPOCH.

Provides handy shortcuts¶

Instanciation¶

You can instanciate a new Time with several formats:

With a string (provided you give a timezone in the string or as hint_src_tz):

>>> Time("2010-10-01 10:00+01:00")
<Time 2010-10-01 10:00:00+01:00>
>>> Time("2010-10-20", hint_src_tz=UTC())
<Time 2010-10-20 00:00:00+00:00>

With a partial string, remember the we are in:

>>> Time.now()
<Time 1970-01-01 00:00:00+00:00>
>>> Time("10h00", relative=Time.now())
<Time 1970-01-01 10:00:00+00:00>

If not specified, it uses Time.now() as reference date to infer missing element of the given date string:

>>> Time("Thu 10:36", hint_src_tz=UTC())
<Time 1970-01-01 10:36:00+00:00>

As it remains a datetime.datetime sub-class you can instanciate it like a datetime:

>>> Time(1980, 1, 2)
<Time 1980-01-02 00:00:00+00:00>

Properties¶

Getting timestamp from a datetime was nightmarish. Now simply:

>>> t = Time(1980, 1, 1)
>>> t.timestamp
315532800

or (as an alias):

>>> t.ts
315532800

And of course:

>>> Time.fromtimestamp(t.timestamp) == t
True

As a matter of fact, .fromtimestamp is equivalent to .utcfromtimestamp. (Let’s repeat it: timestamp should ALWAYS be considered UTC). If you want system local time from a timestamp you could:

>>> Time.fromtimestamp(t.timestamp).local
<Time 1980-01-01 00:05:00+00:05>

Getting the local/utc zoned time (not changing the time, only the timezone):

>>> t.local, t.utc
(<Time 1980-01-01 00:05:00+00:05>, <Time 1980-01-01 00:00:00+00:00>)

So to make sure you understood:

>>> t.local == t.utc
True
>>> t.local.timestamp == t.timestamp
True

This was to illustrate the fact that the time didn’t change.

Getting some common representations:

>>> t.iso
'1980-01-01 00:00:00+00:00'

This last string formatting of a date is complete, and you can easily get a accurate sact.epoch.Time object with it, by direct instanciation:

>>> Time(t.iso) == t
True

Warning, these representation will loose the tz info:

>>> t.short        ## warning: this representation does not include tz info
'1980-01-01 00:00:00'
>>> t.local.short  ## warning: this representation does not include tz info
'1980-01-01 00:05:00'
>>> t.short_short  ## warning: this representation does not include tz info
'1980-01-01 00:00'

As they don’t provide the timezone’s information, you can’t instanciate them directly without providing an hint thanks to giving the timezone, or by giving a relative datetime from which the timezone will be taken:

>>> Time(t.short)
Traceback (most recent call last):
...
ValueError: No timezone hinted, nor found.
>>> Time(t.short, hint_src_tz=UTC())
<Time 1980-01-01 00:00:00+00:00>

strptime¶

Time.strptime() was modified from the datetime.datetime version, it now asks for the source timezone info:

>>> Time.strptime('15:08', '%H:%M', hint_src_tz=TzLocal())
<Time 1900-01-01 15:03:00+00:00>

Notice that the Time instance is in UTC, so 15:08 in implicit local time zone, became 15:03 in UTC. If you wanted the local Time instance instead:

>>> Time.strptime('15:08', '%H:%M', hint_src_tz=TzLocal()).local
<Time 1900-01-01 15:08:00+00:05>

The local timezone detection is of course divertable, and you can also set it thanks to a new argument named hint_src_tz:

>>> Time.strptime('15:08', '%H:%M', hint_src_tz=UTC())
<Time 1900-01-01 15:08:00+00:00>

Notice also, that we didn’t specify 1900 as the year, but it was used. In Time.strptime() you can actually set the reference:

>>> t = Time(2000, 1, 1)
>>> Time.strptime('15:08', '%H:%M', hint_src_tz=UTC(), relative=t)
<Time 2000-01-01 15:08:00+00:00>

How to unregister¶

You can unregister the diverting mecanism:

>>> TzLocal()
<TimeZone: Test>
>>> gsm.unregisterUtility(clock)
True
>>> gsm.unregisterUtility(testTimeZone, ITimeZone, 'local')
True
>>> TzLocal()
<TimeZone: System>

INSTALLATION¶

For installation issue please refer to INSTALL.rst file.

DEVELOPPEMENT¶

You can test or use this code simply by launching:

python bootstrap.py
buildout

This will install all dependency needed by this code to start coding.

TEST¶

Test framework is available through standard z3c.testsetup mecanism:

bin/test

DOC¶

Complete documentation can be generated thanks to:

bin/doc