5.1.4 datetime Objects

Python 2.5

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5.1.4 `datetime` Objects

A datetime object is a single object containing all the information from a date object and a time object. Like a date object, datetime assumes the current Gregorian calendar extended in both directions; like a time object, datetime assumes there are exactly 3600*24 seconds in every day.

Constructor:

class datetime( year, month, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]])

The year, month and day arguments are required. tzinfo may be None, or an instance of a tzinfo subclass. The remaining arguments may be ints or longs, 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
0 <= microsecond < 1000000

If an argument outside those ranges is given, ValueError is raised.

Other constructors, all class methods:

today( ): Return the current local datetime, with tzinfo None. This is equivalent to datetime.fromtimestamp(time.time()). See also now(), fromtimestamp().

now( [tz]): Return the current local date and time. If optional argument tz is None or not specified, this is like today(), but, if possible, supplies more precision than can be gotten from going through a time.time() timestamp (for example, this may be possible on platforms supplying the C gettimeofday() function).
Else tz must be an instance of a class tzinfo subclass, and the current date and time are converted to tz's time zone. In this case the result is equivalent to tz.fromutc(datetime.utcnow().replace(tzinfo=tz)). See also today(), utcnow().

utcnow( ): Return the current UTC date and time, with tzinfo None. This is like now(), but returns the current UTC date and time, as a naive datetime object. See also now().

fromtimestamp( timestamp[, tz])

Return the local date and time corresponding to the POSIX timestamp, such as is returned by time.time(). If optional argument tz is None or not specified, the timestamp is converted to the platform's local date and time, and the returned datetime object is naive.

Else tz must be an instance of a class tzinfo subclass, and the timestamp is converted to tz's time zone. In this case the result is equivalent to tz.fromutc(datetime.utcfromtimestamp(timestamp).replace(tzinfo=tz)).

fromtimestamp() may raise ValueError, if the timestamp is out of the range of values supported by the platform C localtime() or gmtime() functions. It's common for this to be restricted to years in 1970 through 2038. Note that on non-POSIX systems that include leap seconds in their notion of a timestamp, leap seconds are ignored by fromtimestamp(), and then it's possible to have two timestamps differing by a second that yield identical datetime objects. See also utcfromtimestamp().

utcfromtimestamp( timestamp): Return the UTC datetime corresponding to the POSIX timestamp, with tzinfo None. This may raise ValueError, if the timestamp is out of the range of values supported by the platform C gmtime() function. It's common for this to be restricted to years in 1970 through 2038. See also fromtimestamp().

fromordinal( ordinal): 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, second and microsecond of the result are all 0, and tzinfo is None.

combine( date, time): Return a new datetime object whose date members are equal to the given date object's, and whose time and tzinfo members are equal to the given time object's. For any datetime object d, d == datetime.combine(d.date(), d.timetz()). If date is a datetime object, its time and tzinfo members are ignored.

strptime( date_string, format): Return a datetime corresponding to date_string, parsed according to format. This is equivalent to datetime(*(time.strptime(date_string, format)[0:6])). ValueError is raised if the date_string and format can't be parsed by time.strptime() or if it returns a value which isn't a time tuple.
New in version 2.5.

Class attributes:

min: The earliest representable datetime, datetime(MINYEAR, 1, 1, tzinfo=None).

max: The latest representable datetime, datetime(MAXYEAR, 12, 31, 23, 59, 59, 999999, tzinfo=None).

resolution: The smallest possible difference between non-equal datetime objects, timedelta(microseconds=1).

Instance attributes (read-only):

year: Between MINYEAR and MAXYEAR inclusive.

month: Between 1 and 12 inclusive.

day: Between 1 and the number of days in the given month of the given year.

hour: In range(24).

minute: In range(60).

second: In range(60).

microsecond: In range(1000000).

tzinfo: The object passed as the tzinfo argument to the datetime constructor, or None if none was passed.

Supported operations:

Operation	Result
`datetime2 = datetime1 + timedelta`	(1)
`datetime2 = datetime1 - timedelta`	(2)
`timedelta = datetime1 - datetime2`	(3)
`datetime1 < datetime2`	Compares `datetime` to `datetime`. (4)

(1)

datetime2 is a duration of timedelta removed from datetime1, moving forward in time if timedelta.days > 0, or backward if timedelta.days < 0. The result has the same tzinfo member as the input datetime, and datetime2 - datetime1 == timedelta after. OverflowError is raised if datetime2.year would be smaller than MINYEAR or larger than MAXYEAR. Note that no time zone adjustments are done even if the input is an aware object.

(2)

Computes the datetime2 such that datetime2 + timedelta == datetime1. As for addition, the result has the same tzinfo member as the input datetime, and no time zone adjustments are done even if the input is aware. This isn't quite equivalent to datetime1 + (-timedelta), because -timedelta in isolation can overflow in cases where datetime1 - timedelta does not.

(3)

Subtraction of a datetime from a datetime 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 tzinfo member, the tzinfo members 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 tzinfo members, a-b acts as if a and b were first converted to naive UTC datetimes first. The result is (a.replace(tzinfo=None) - a.utcoffset()) - (b.replace(tzinfo=None) - b.utcoffset()) except that the implementation never overflows.

(4)

datetime1 is considered less than datetime2 when datetime1 precedes datetime2 in time.

If one comparand is naive and the other is aware, TypeError is raised. If both comparands are aware, and have the same tzinfo member, the common tzinfo member is ignored and the base datetimes are compared. If both comparands are aware and have different tzinfo members, the comparands are first adjusted by subtracting their UTC offsets (obtained from self.utcoffset()). Note: In order to stop comparison from falling back to the default scheme of comparing object addresses, datetime comparison normally raises TypeError if the other comparand isn't also a datetime object. However, NotImplemented is returned instead if the other comparand has a timetuple attribute. This hook gives other kinds of date objects a chance at implementing mixed-type comparison. If not, when a datetime object is compared to an object of a different type, TypeError is raised unless the comparison is == or !=. The latter cases return False or True, respectively.

datetime objects can be used as dictionary keys. In Boolean contexts, all datetime objects are considered to be true.

Instance methods:

date( ): Return date object with same year, month and day.

time( ): Return time object with same hour, minute, second and microsecond. tzinfo is None. See also method timetz().

timetz( ): Return time object with same hour, minute, second, microsecond, and tzinfo members. See also method time().

replace( [year[, month[, day[, hour[, minute[, second[, microsecond[, tzinfo]]]]]]]]): Return a datetime with the same members, except for those members 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 members.

astimezone( tz)

Return a datetime object with new tzinfo member tz, adjusting the date and time members so the result is the same UTC time as self, but in tz's local time.

tz must be an instance of a tzinfo subclass, and its utcoffset() and dst() methods must not return None. self must be aware (self.tzinfo must not be None, and self.utcoffset() must not return None).

If self.tzinfo is tz, self.astimezone(tz) is equal to self: no adjustment of date or time members is performed. Else the result is local time in time zone tz, representing the same UTC time as self: after astz = dt.astimezone(tz), astz - astz.utcoffset() will usually have the same date and time members as dt - dt.utcoffset(). The discussion of class tzinfo explains the cases at Daylight Saving Time transition boundaries where this cannot be achieved (an issue only if tz models both standard and daylight time).

If you merely want to attach a time zone object tz to a datetime dt without adjustment of date and time members, use dt.replace(tzinfo=tz). If you merely want to remove the time zone object from an aware datetime dt without conversion of date and time members, use dt.replace(tzinfo=None).

Note that the default tzinfo.fromutc() method can be overridden in a tzinfo subclass to affect the result returned by astimezone(). Ignoring error cases, astimezone() acts like:

  def astimezone(self, tz):
      if self.tzinfo is tz:
          return self
      # Convert self to UTC, and attach the new time zone object.
      utc = (self - self.utcoffset()).replace(tzinfo=tz)
      # Convert from UTC to tz's local time.
      return tz.fromutc(utc)

utcoffset( ): If tzinfo is None, returns None, else returns self.tzinfo.utcoffset(self), and raises an exception if the latter doesn't return None, or a timedelta object representing a whole number of minutes with magnitude less than one day.

dst( ): If tzinfo is None, returns None, else returns self.tzinfo.dst(self), and raises an exception if the latter doesn't return None, or a timedelta object representing a whole number of minutes with magnitude less than one day.

tzname( ): If tzinfo is None, returns None, else returns self.tzinfo.tzname(self), raises an exception if the latter doesn't return None or a string object,

timetuple( ): Return a time.struct_time such as returned by time.localtime(). d.timetuple() is equivalent to time.struct_time((d.year, d.month, d.day, d.hour, d.minute, d.second, d.weekday(), d.toordinal() - date(d.year, 1, 1).toordinal() + 1, dst)) The tm_isdst flag of the result is set according to the dst() method: tzinfo is None or dst() returns None, tm_isdst is set to -1; else if dst() returns a non-zero value, tm_isdst is set to 1; else tm_isdst is set to 0.

utctimetuple( ): If datetime instance d is naive, this is the same as d.timetuple() except that tm_isdst is forced to 0 regardless of what d.dst() returns. DST is never in effect for a UTC time.
If d is aware, d is normalized to UTC time, by subtracting d.utcoffset(), and a time.struct_time for the normalized time is returned. tm_isdst is forced to 0. Note that the result's tm_year member may be MINYEAR-1 or MAXYEAR+1, if d.year was MINYEAR or MAXYEAR and UTC adjustment spills over a year boundary.

toordinal( ): Return the proleptic Gregorian ordinal of the date. The same as self.date().toordinal().

weekday( ): Return the day of the week as an integer, where Monday is 0 and Sunday is 6. The same as self.date().weekday(). See also isoweekday().

isoweekday( ): Return the day of the week as an integer, where Monday is 1 and Sunday is 7. The same as self.date().isoweekday(). See also weekday(), isocalendar().

isocalendar( ): Return a 3-tuple, (ISO year, ISO week number, ISO weekday). The same as self.date().isocalendar().

isoformat( [sep])

Return a string representing the date and time in ISO 8601 format, YYYY-MM-DDTHH:MM:SS.mmmmmm or, if microsecond is 0, YYYY-MM-DDTHH:MM:SS

If utcoffset() does not return None, a 6-character string is appended, giving the UTC offset in (signed) hours and minutes: YYYY-MM-DDTHH:MM:SS.mmmmmm+HH:MM or, if microsecond is 0 YYYY-MM-DDTHH:MM:SS+HH:MM

The optional argument sep (default 'T') is a one-character separator, placed between the date and time portions of the result. For example,

>>> from datetime import tzinfo, timedelta, datetime
>>> class TZ(tzinfo):
...     def utcoffset(self, dt): return timedelta(minutes=-399)
...
>>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
'2002-12-25 00:00:00-06:39'

__str__( ): For a datetime instance d, str(d) is equivalent to d.isoformat(' ').

ctime( ): Return a string representing the date and time, for example datetime(2002, 12, 4, 20, 30, 40).ctime() == 'Wed Dec 4 20:30:40 2002'. d.ctime() is equivalent to time.ctime(time.mktime(d.timetuple())) on platforms where the native C ctime() function (which time.ctime() invokes, but which datetime.ctime() does not invoke) conforms to the C standard.

strftime( format): Return a string representing the date and time, controlled by an explicit format string. See section 5.1.7 - strftime() behavior.

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