Date and time¶
This module supplies classes for manipulating dates, times, and deltas. It represents a minimalistic implementation of Python module datetime.
datetime
objects may be categorized as “aware” or “naive” depending on whether or not they include timezone information. An aware object can locate itself relative to other aware objects. An aware object represents a specific moment in time that is not open to interpretation.
A naive object does not contain enough information to unambiguously locate itself relative to other datetime
objects. Whether a naive object represents Coordinated Universal Time (UTC), local time, or time in some other timezone is purely up to the program, just like it is up to the program whether a particular number represents metres, miles, or mass. Naive objects are easy to understand and to work with, at the cost of ignoring some aspects of reality.
For applications requiring aware objects, datetime
objects have an optional time zone information attribute, tzinfo, that can be set to an instance of a timezone
class. These objects capture information about the offset from UTC time and the time zone name.
The following classes are provided:
timedelta Objects¶
A timedelta
object represents a duration, the difference between two dates or times. With respect to the Python module datetime, this implementation is constrained as follows:
- Minimum resolution is 1 second, instead of 1 microsecond.
- Arithmetic is done via direct function calls (
add()
vs__add__()
) due to Zerynth’s limits.
Class attributes¶
timedelta.``MINYEAR
The year of timedelta.min
, i.e. timedelta.min.tuple()[1] // (365×24×60×60) == -34
.
timedelta.``MAXYEAR
The year of timedelta.max
, i.e. timedelta.max.tuple()[1] // (365×24×60×60) == 34
.
timedelta.``min
The most negative timedelta
object, timedelta(-2**30)
.
timedelta.``max
The most positive timedelta
object, timedelta(2**30 - 1)
.
timedelta.``resolution
The smallest possible difference between non-equal timedelta
objects, timedelta(seconds=1)
.
Class methods¶
classtimedelta
(hours=0, minutes=0, seconds=0, days=0, weeks=0)
All arguments are optional and default to 0
. Arguments may be integers or floats, and may be positive or negative. Only seconds are stored internally. Arguments are converted to those units:
- A minute is converted to 60 seconds.
- An hour is converted to 3600 seconds.
- A week is converted to 7 days.
If no argument is a float, the conversion and normalization processes are exact (no information is lost).
total_seconds
()
Return the total number of seconds contained in the duration.
add
(other)
Return the difference between two durations.
mul
(other)
Return a delta multiplied by an integer or float. The result is rounded to the nearest second using round-half-to-even.
truediv
(other)
When other is a float or an integer, returns a delta divided by other. The result is rounded to the nearest multiple of timedelta.resolution using round-half-to-even.
When other is a delta, division of overall duration by interval unit other. Returns a float object.
floordiv
(other)
The floor is computed and the remainder (if any) is thrown away. When other is a delta, an integer is returned.
mod
(other)
The remainder is computed as a timedelta
object.
divmod
(other)
Computes the quotient and the remainder: q = td1.floordiv(td2)
and r = td1.mod(td2)
. q
is an integer and r
is a timedelta
object.
neg
()
Equivalent to td1.mul(-1)
.
eq
(other)
Equivalent to td1.total_seconds() == td2.totalseconds()
.
le
(other)
Equivalent to td1.total_seconds() <= td2.totalseconds()
.
lt
(other)
Equivalent to td1.total_seconds() < td2.totalseconds()
.
ge
(other)
Equivalent to td1.total_seconds() >= td2.totalseconds()
.
gt
(other)
Equivalent to td1.total_seconds() > td2.totalseconds()
.
bool
()
Return False
when duration is 0
.
abs
()
Return a positive delta.
tuple
(sign_pos='')
Return the tuple (sign, days, hours, minutes, seconds)
, where sign
is -
if delta is negative, sign_pos otherwise.
Examples of usage¶
An example of normalization:
import datetime.timedelta
# Components of another_year add up to exactly 365 days
year = timedelta(days=365)
another_year = timedelta(weeks=40, days=84, hours=23, minutes=50, seconds=600)
print(year.eq(another_year)) # True
print(year.total_seconds()) # 31536000
Examples of timedelta arithmetic:
import datetime.timedelta
year = timedelta(days=365)
ten_years = year.mul(10)
print(ten_years) # 3650d 00:00:00
nine_years = ten_years.sub(year)
print(nine_years) # 3285d 00:00:00
three_years = nine_years.floordiv(3)
print(three_years) # 1095d 00:00:00
timezone Objects¶
The timezone
class represents a timezone defined by a fixed offset from UTC. Define a subclass of timezone
to capture information about a particular time zone.
An instance of timezone
can be passed to the constructors for datetime
. The latter objects view their attributes as being in local time, and the timezone
object supports methods revealing offset of local time from UTC, the name of the time zone, and DST offset, all relative to a date-time object passed to them.
Methods to customize¶
A subclass of timezone
may need to override the following methods. Exactly which methods are needed depends on the uses made of aware datetime
objects. If in doubt, simply implement all of them.
utcoffset
(dt)
Return offset of local time from UTC, as a timedelta
object that is positive east of UTC. If local time is west of UTC, this should be negative.
This represents the total offset from UTC; for example, if a timezone
object represents both time zone and DST adjustments, timezone.utcoffset()
should return their sum. If the UTC offset isn’t known, return None
. Else the value returned must be a timedelta
object strictly between timedelta(hours=-24)
and timedelta(hours=24)
(the magnitude of the offset must be less than one day). Most implementations of timezone.utcoffset()
will probably look like one of these two:
return CONSTANT # fixed-offset class return CONSTANT + self.dst(dt) # daylight-aware class
If timezone.utcoffset()
does not return None
, timezone.dst()
should not return None either.
The default implementation of timezone.utcoffset()
returns the sum of time zone and DST adjustments, if available.
dst
(dt)
Return the daylight saving time (DST) adjustment, as a timedelta
object or None
if DST information isn’t known.
Return timedelta(0)
if DST is not in effect. If DST is in effect, return the offset as a timedelta
object (see timezone.utcoffset()
for details). Note that DST offset, if applicable, has already been added to the UTC offset returned by timezone.utcoffset()
, so there’s no need to consult timezone.dst()
unless you’re interested in obtaining DST info separately.
Most implementations of timezone.dst()
will probably look like one of these two:
def dst(self, dt):
# a fixed-offset class: doesn't account for DST
return timedelta(0)
or:
def dst(self, dt):
# Code to set dston and dstoff to the time zone's DST
# transition times based on the input *dt*'s year, and
# expressed in standard local time.
dt_ = dt.replace(tzinfo=None)
if dt_.ge(dston) and dt_.lt(dstoff):
return timedelta(hours=1)
else:
return timedelta(0)
The default implementation of timezone.dst()
returns None
.
tzname
(dt)
Return the time zone name corresponding to the datetime
object dt, as a string. Nothing about string names is defined by the datetime
module, and there’s no requirement that it mean anything in particular. For example, “GMT”, “UTC”, “-500”, “-5:00”, “EDT”, “US/Eastern”, “America/New York” are all valid replies. Return None
if a string name isn’t known. Note that this is a method rather than a fixed string primarily because some timezone
subclasses will wish to return different names depending on the specific value of dt passed, especially if the timezone
class is accounting for daylight time.
The default implementation of timezone.tzname()
returns the fixed value specified when the timezone
instance is constructed. If name is not provided in the constructor, the name returned by tzname()
is generated from the value of the offset
as follows. If offset is timedelta(0)
, the name is “UTC”, otherwise it returns the string provided by timezone.isoformat()
method.
These methods are called by a datetime
object, in response to their methods of the same names. A datetime
object passes self as dt argument.
Class attributes¶
timezone.``utc
The UTC timezone, timezone(timedelta(0))
.
Class methods¶
classtimezone
(offset, name=None)
The offset argument must be specified as a timedelta
object representing the difference between the local time and UTC. It must be strictly between timedelta(hours=-24)
and timedelta(hours=24)
, otherwise ValueError
is raised.
The name argument is optional. If specified it must be a string that will be used as the value returned by the datetime.tzname()
method.
isoformat
(dt)
Return a string in the format UTC±HH:MM
, where ±
is the sign of offset from UTC, HH
and MM
are two digits of offset’s hours and offset’s minutes respectively. If offset is timedelta(0)
, “UTC” is returned.
If utc is False
, this method always returns ±HH:MM
.
dt is needed in determining the right offset; it can be None
.
Examples of usage¶
Central European Time (CET), used in most parts of Europe and a few North African countries, is a standard time which is 1 hour ahead of Coordinated Universal Time (UTC). As of 2011, all member states of the European Union observe summer time; those that during the winter use CET use Central European Summer Time (CEST) (or: UTC+02:00, daylight saving time) in summer (from last Sunday of March to last Sunday of October).
import datetime
class cet(datetime.timezone):
def __init__(self):
datetime.timezone.__init__(self, datetime.timedelta(hours=1))
def dst(self, dt):
return datetime.timedelta(hours=1) if self.isdst(dt) else datetime.timedelta(0)
def tzname(self, dt):
return 'CEST' if self.isdst(dt) else 'CET'
def isdst(self, dt):
if dt is None:
return False
dt_ = dt.replace(tzinfo=None)
year = dt.tuple()[0]
day = 31 - (5*year//4 + 4) % 7 # last Sunday of March
dst = dt_.replace(month=3, day=day)
if dt_.lt(dst):
return False
day = 31 - (5*year//4 + 1) % 7 # last Sunday of October
dst = dt_.replace(month=10, day=day)
if dt_.lt(dst):
return True
return False
tz = cet()
print(tz.isoformat(datetime(2011, 1, 1))) # UTC+01:00
print(tz.tzname (datetime(2011, 1, 1))) # CET
print(tz.isoformat(datetime(2011, 8, 1))) # UTC+02:00
print(tz.tzname (datetime(2011, 8, 1))) # CEST
datetime Objects¶
A datetime
object is a single object containing all the information for specifying an absolute date and time point.
datetime
assumes the current Gregorian calendar extended in both directions, past and future. January 1 of year 1 is called day number 1, January 2 of year 1 is called day number 2, and so on.
datetime
assumes there are exactly 3600*24 seconds in every day and subject to adjustment via a timezone
object.
Constructors¶
classdatetime
(self, year, month, day, hour=0, minute=0, second=0, tzinfo=None)
The year, month and day arguments are required. tzinfo may be None
, or an instance of a timezone
class. The remaining arguments must be integers in the following ranges:
MINYEAR <= year <= MAXYEAR
,1 <= month <= 12
,1 <= day <= number of days in the given month and year
,0 <= hour < 24
,0 <= minute < 60
,0 <= second < 60
,
If an argument outside those ranges is given, ValueError
is raised.
fromisoformat
(date_string)
Return a datetime
corresponding to a date_string in the format emitted by datetime.isoformat()
.
Specifically, this function supports strings in the format:
YYYY-MM-DD[*HH[:MM[:SS[.fff[fff]]]][+HH:MM[:SS[.ffffff]]]]
where *
can match any single character.
fromordinal
(n)
Return the datetime
corresponding to the proleptic Gregorian ordinal, where January 1 of year 1 has ordinal 1. ValueError
is raised unless 1 <= ordinal <= datetime.max.toordinal()
. The hour, minute and second of the result are all 0, and tzinfo is None
.
Class attributes¶
datetime.``MINYEAR
The smallest year number allowed in a datetime
object. datetime.MINYEAR
is 1
.
datetime.``MAXYEAR
The largest year number allowed in a datetime
object. datetime.MAXYEAR
is 9999
.
Class methods¶
add
(other)
In the expression datetime2 = datetime1.add(timedelta)
, datetime2
is a duration of timedelta
removed from datetime1
, moving forward in time if timedelta > 0
, or backward if timedelta < 0
. The result has the same timezone
attribute as the input datetime1
, and datetime2 - datetime1 == timedelta
after.
Note that no time zone adjustments are done even if the input is an aware object.
sub
(other)
If other is an instance of timedelta
, the expression datetime2 = datetime1.sub(timedelta)
computes the datetime2
such that datetime2 + timedelta == datetime1
. As for addition, the result has the same timezone
attribute as the input datetime1
, and no time zone adjustments are done even if the input is aware.
If other is an instance of datetime
, subtraction timedelta = datetime2.sub(datetime1)
is defined only if both operands are naive, or if both are aware. If one is aware and the other is naive, TypeError
is raised.
If both are naive, or both are aware and have the same timezone
attribute, the timezone
attributes are ignored, and the result is a timedelta
object t such that datetime2 + t == datetime1
. No time zone adjustments are done in this case.
If both are aware and have different timezone
attributes, a-b
acts as if a and b were first converted to naive UTC datetimes first.
lt
(other)
Equivalent to dt1.toordinal() < dt2.toordinal()
.
lt
(other)
Equivalent to dt1.toordinal() <= dt2.toordinal()
.
lt
(other)
Equivalent to dt1.toordinal() == dt2.toordinal()
.
lt
(other)
Equivalent to dt1.toordinal() >= dt2.toordinal()
.
lt
(other)
Equivalent to dt1.toordinal() > dt2.toordinal()
.
utcoffset
()
If tzinfo is None
, returns None
, else returns a timedelta
object with magnitude less than one day.
replace
(year=None, month=None, day=None, hour=None, minute=None, second=None, tzinfo=True)
Return a datetime
with the same attributes, except for those attributes given new values by whichever keyword arguments are specified. Note that tzinfo=None
can be specified to create a naive datetime
from an aware datetime
with no conversion of date and time data.
astimezone
(tz)
Return a datetime
object with new tzinfo attribute tz, adjusting the date and time data so the result is the same UTC time as self, but in tz’s local time. self must be aware.
If you merely want to attach a timezone
object tz to a datetime
dt without adjustment of date and time data, use dt.replace(tzinfo=tz)
. If you merely want to remove the timezone
object from an aware datetime
dt without conversion of date and time data, use dt.replace(tzinfo=None)
.
isoformat
(sep='T')
Return a string representing the date and time in ISO 8601 format YYYY-MM-DDTHH:MM:SS
. If datetime.utcoffset()
does not return None
, a string is appended, giving the UTC offset: YYYY-MM-DDTHH:MM:SS+HH:MM
.
toordinal
()
Return the proleptic Gregorian ordinal of the date.
isoweekday
()
Return the day of the week as an integer, where Monday is 1 and Sunday is 7. For example, date(2002, 12, 4).isoweekday() == 3
, a Wednesday.
tuple
()
Return the tuple (year, month, day, hour, minute, second, tzinfo)
.
Examples of usage¶
Examples of working with datetime
objects:
from datetime import timedelta, timezone, datetime, fromisoformat
print(datetime(2005, 7, 14, 12, 30)) # 2005-07-14 12:30:00
dt = fromisoformat('2006-11-21 16:30+01:00')
print(dt.add(timedelta(hours=23))) # 2006-11-22 15:30:00+01:00
tz1 = timezone(timedelta(hours=4, minutes=30))
print(tz1) # UTC+04:30
dt = datetime(1900, 11, 21, 3, 30, tzinfo=tz1)
print(dt) # 1900-11-21 03:30:00+04:30
print(dt.astimezone(timezone.utc)) # 1900-11-20 23:00:00+00:00