datetime — Basic date and time types¶

Aware and Naive Objects¶

Date and time objects may be categorized as “aware” or “naive” depending on whether or not they include time zone information.

With sufficient knowledge of applicable algorithmic and political time adjustments, such as time zone and daylight saving time 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. [1]

A naive object does not contain enough information to unambiguously locate itself relative to other date/time objects. Whether a naive object represents Coordinated Universal Time (UTC), local time, or time in some other time zone 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 and time objects have an optional time zone information attribute, tzinfo, that can be set to an instance of a subclass of the abstract tzinfo class. These tzinfo objects capture information about the offset from UTC time, the time zone name, and whether daylight saving time is in effect.

Only one concrete tzinfo class, the timezone class, is supplied by the datetime module. The timezone class can represent simple time zones with fixed offsets from UTC, such as UTC itself or North American EST and EDT time zones. Supporting time zones at deeper levels of detail is up to the application. The rules for time adjustment across the world are more political than rational, change frequently, and there is no standard suitable for every application aside from UTC.

Constants¶

The datetime module exports the following constants:

datetime.MINYEAR¶

The smallest year number allowed in a date or datetime object. MINYEAR is 1.

datetime.MAXYEAR¶

The largest year number allowed in a date or datetime object. MAXYEAR is 9999.

datetime.UTC¶

Alias for the UTC time zone singleton datetime.timezone.utc.

Added in version 3.11.

Available Types¶

class datetime.date

An idealized naive date, assuming the current Gregorian calendar always was, and always will be, in effect. Attributes: year, month, and day.

class datetime.time

An idealized time, independent of any particular day, assuming that every day has exactly 24*60*60 seconds. (There is no notion of “leap seconds” here.) Attributes: hour, minute, second, microsecond, and tzinfo.

class datetime.datetime

A combination of a date and a time. Attributes: year, month, day, hour, minute, second, microsecond, and tzinfo.

class datetime.timedelta

A duration expressing the difference between two datetime or date instances to microsecond resolution.

class datetime.tzinfo

An abstract base class for time zone information objects. These are used by the datetime and time classes to provide a customizable notion of time adjustment (for example, to account for time zone and/or daylight saving time).

class datetime.timezone

A class that implements the tzinfo abstract base class as a fixed offset from the UTC.

Added in version 3.2.

Objects of these types are immutable.

Subclass relationships:

object
    timedelta
    tzinfo
        timezone
    time
    date
        datetime

timedelta Objects¶

A timedelta object represents a duration, the difference between two datetime or date instances.

class datetime.timedelta(days=0, seconds=0, microseconds=0, milliseconds=0, minutes=0, hours=0, weeks=0)¶

All arguments are optional and default to 0. Arguments may be integers or floats, and may be positive or negative.

Only days, seconds and microseconds are stored internally. Arguments are converted to those units:

• A millisecond is converted to 1000 microseconds.

• A minute is converted to 60 seconds.

• An hour is converted to 3600 seconds.

• A week is converted to 7 days.

and days, seconds and microseconds are then normalized so that the representation is unique, with

• 0 <= microseconds < 1000000

• 0 <= seconds < 3600*24 (the number of seconds in one day)

• -999999999 <= days <= 999999999

The following example illustrates how any arguments besides days, seconds and microseconds are “merged” and normalized into those three resulting attributes:

>>> from datetime import timedelta
>>> delta = timedelta(
...     days=50,
...     seconds=27,
...     microseconds=10,
...     milliseconds=29000,
...     minutes=5,
...     hours=8,
...     weeks=2
... )
>>> # Only days, seconds, and microseconds remain
>>> delta
datetime.timedelta(days=64, seconds=29156, microseconds=10)

If any argument is a float and there are fractional microseconds, the fractional microseconds left over from all arguments are combined and their sum is rounded to the nearest microsecond using round-half-to-even tiebreaker. If no argument is a float, the conversion and normalization processes are exact (no information is lost).

If the normalized value of days lies outside the indicated range, OverflowError is raised.

Note that normalization of negative values may be surprising at first. For example:

>>> from datetime import timedelta
>>> d = timedelta(microseconds=-1)
>>> (d.days, d.seconds, d.microseconds)
(-1, 86399, 999999)

Since the string representation of timedelta objects can be confusing, use the following recipe to produce a more readable format:

>>> def pretty_timedelta(td):
...     if td.days >= 0:
...         return str(td)
...     return f'-({-td!s})'
...
>>> d = timedelta(hours=-1)
>>> str(d)  # not human-friendly
'-1 day, 23:00:00'
>>> pretty_timedelta(d)
'-(1:00:00)'

Class attributes:

timedelta.min¶

The most negative timedelta object, timedelta(-999999999).

timedelta.max¶

The most positive timedelta object, timedelta(days=999999999, hours=23, minutes=59, seconds=59, microseconds=999999).

timedelta.resolution¶

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

Note that, because of normalization, timedelta.max is greater than -timedelta.min. -timedelta.max is not representable as a timedelta object.

Instance attributes (read-only):

timedelta.days¶

Between -999,999,999 and 999,999,999 inclusive.

timedelta.seconds¶

Between 0 and 86,399 inclusive.

Caution

It is a somewhat common bug for code to unintentionally use this attribute when it is actually intended to get a total_seconds() value instead:

>>> from datetime import timedelta
>>> duration = timedelta(seconds=11235813)
>>> duration.days, duration.seconds
(130, 3813)
>>> duration.total_seconds()
11235813.0

timedelta.microseconds¶

Between 0 and 999,999 inclusive.

Supported operations:

Notes:

1. This is exact but may overflow.

2. This is exact and cannot overflow.

3. Division by zero raises ZeroDivisionError.

4. -timedelta.max is not representable as a timedelta object.

5. String representations of timedelta objects are normalized similarly to their internal representation. This leads to somewhat unusual results for negative timedeltas. For example:

   >>> timedelta(hours=-5)
   datetime.timedelta(days=-1, seconds=68400)
   >>> print(_)
   -1 day, 19:00:00
   

6. The expression t2 - t3 will always be equal to the expression t2 + (-t3) except when t3 is equal to timedelta.max; in that case the former will produce a result while the latter will overflow.

In addition to the operations listed above, timedelta objects support certain additions and subtractions with date and datetime objects (see below).

timedelta objects support equality and order comparisons.

In Boolean contexts, a timedelta object is considered to be true if and only if it isn’t equal to timedelta(0).

Instance methods:

timedelta.total_seconds()¶

Return the total number of seconds contained in the duration. Equivalent to td / timedelta(seconds=1). For interval units other than seconds, use the division form directly (e.g. td / timedelta(microseconds=1)).

Note that for very large time intervals (greater than 270 years on most platforms) this method will lose microsecond accuracy.

Added in version 3.2.

>>> # Components of another_year add up to exactly 365 days
>>> from datetime import timedelta
>>> year = timedelta(days=365)
>>> another_year = timedelta(weeks=40, days=84, hours=23,
...                          minutes=50, seconds=600)
>>> year == another_year
True
>>> year.total_seconds()
31536000.0

>>> from datetime import timedelta
>>> year = timedelta(days=365)
>>> ten_years = 10 * year
>>> ten_years
datetime.timedelta(days=3650)
>>> ten_years.days // 365
10
>>> nine_years = ten_years - year
>>> nine_years
datetime.timedelta(days=3285)
>>> three_years = nine_years // 3
>>> three_years, three_years.days // 365
(datetime.timedelta(days=1095), 3)

date Objects¶

A date object represents a date (year, month and day) in an idealized calendar, the current Gregorian calendar indefinitely extended in both directions.

January 1 of year 1 is called day number 1, January 2 of year 1 is called day number 2, and so on. [2]

class datetime.date(year, month, day)¶

All arguments are required. 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

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

Other constructors, all class methods:

classmethod date.today()¶

Return the current local date.

This is equivalent to date.fromtimestamp(time.time()).

classmethod date.fromtimestamp(timestamp)¶

Return the local date corresponding to the POSIX timestamp, such as is returned by time.time().

This may raise OverflowError, if the timestamp is out of the range of values supported by the platform C localtime() function, and OSError on localtime() failure. It’s common for this to be restricted to years from 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().

Changed in version 3.3: Raise OverflowError instead of ValueError if the timestamp is out of the range of values supported by the platform C localtime() function. Raise OSError instead of ValueError on localtime() failure.

classmethod date.fromordinal(ordinal)¶

Return the date corresponding to the proleptic Gregorian ordinal, where January 1 of year 1 has ordinal 1.

ValueError is raised unless 1 <= ordinal <= date.max.toordinal(). For any date d, date.fromordinal(d.toordinal()) == d.

classmethod date.fromisoformat(date_string)¶

Return a date corresponding to a date_string given in any valid ISO 8601 format, with the following exceptions:

1. Reduced precision dates are not currently supported (YYYY-MM, YYYY).

2. Extended date representations are not currently supported (±YYYYYY-MM-DD).

3. Ordinal dates are not currently supported (YYYY-OOO).

Examples:

>>> from datetime import date
>>> date.fromisoformat('2019-12-04')
datetime.date(2019, 12, 4)
>>> date.fromisoformat('20191204')
datetime.date(2019, 12, 4)
>>> date.fromisoformat('2021-W01-1')
datetime.date(2021, 1, 4)

Added in version 3.7.

Changed in version 3.11: Previously, this method only supported the format YYYY-MM-DD.

classmethod date.fromisocalendar(year, week, day)¶

Return a date corresponding to the ISO calendar date specified by year, week and day. This is the inverse of the function date.isocalendar().

Added in version 3.8.

Class attributes:

date.min¶

The earliest representable date, date(MINYEAR, 1, 1).

date.max¶

The latest representable date, date(MAXYEAR, 12, 31).

date.resolution¶

The smallest possible difference between non-equal date objects, timedelta(days=1).

Instance attributes (read-only):

date.year¶

Between MINYEAR and MAXYEAR inclusive.

date.month¶

Between 1 and 12 inclusive.

date.day¶

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

Supported operations:

Notes:

1. date2 is moved forward in time if timedelta.days > 0, or backward if timedelta.days < 0. Afterward date2 - date1 == timedelta.days. timedelta.seconds and timedelta.microseconds are ignored. OverflowError is raised if date2.year would be smaller than MINYEAR or larger than MAXYEAR.

2. timedelta.seconds and timedelta.microseconds are ignored.

3. This is exact, and cannot overflow. timedelta.seconds and timedelta.microseconds are 0, and date2 + timedelta == date1 after.

4. date objects are equal if they represent the same date.

   date objects that are not also datetime instances are never equal to datetime objects, even if they represent the same date.

5. date1 is considered less than date2 when date1 precedes date2 in time. In other words, date1 < date2 if and only if date1.toordinal() < date2.toordinal().

   Order comparison between a date object that is not also a datetime instance and a datetime object raises TypeError.

In Boolean contexts, all date objects are considered to be true.

Instance methods:

date.replace(year=self.year, month=self.month, day=self.day)¶

Return a new date object with the same values, but with specified parameters updated.

Example:

>>> from datetime import date
>>> d = date(2002, 12, 31)
>>> d.replace(day=26)
datetime.date(2002, 12, 26)

The generic function copy.replace() also supports date objects.

date.timetuple()¶

Return a time.struct_time such as returned by time.localtime().

The hours, minutes and seconds are 0, and the DST flag is -1.

d.timetuple() is equivalent to:

time.struct_time((d.year, d.month, d.day, 0, 0, 0, d.weekday(), yday, -1))

where yday = d.toordinal() - date(d.year, 1, 1).toordinal() + 1 is the day number within the current year starting with 1 for January 1st.

date.toordinal()¶

Return the proleptic Gregorian ordinal of the date, where January 1 of year 1 has ordinal 1. For any date object d, date.fromordinal(d.toordinal()) == d.

date.weekday()¶

Return the day of the week as an integer, where Monday is 0 and Sunday is 6. For example, date(2002, 12, 4).weekday() == 2, a Wednesday. See also isoweekday().

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. See also weekday(), isocalendar().

date.isocalendar()¶

Return a named tuple object with three components: year, week and weekday.

The ISO calendar is a widely used variant of the Gregorian calendar. [3]

The ISO year consists of 52 or 53 full weeks, and where a week starts on a Monday and ends on a Sunday. The first week of an ISO year is the first (Gregorian) calendar week of a year containing a Thursday. This is called week number 1, and the ISO year of that Thursday is the same as its Gregorian year.

For example, 2004 begins on a Thursday, so the first week of ISO year 2004 begins on Monday, 29 Dec 2003 and ends on Sunday, 4 Jan 2004:

>>> from datetime import date
>>> date(2003, 12, 29).isocalendar()
datetime.IsoCalendarDate(year=2004, week=1, weekday=1)
>>> date(2004, 1, 4).isocalendar()
datetime.IsoCalendarDate(year=2004, week=1, weekday=7)

Changed in version 3.9: Result changed from a tuple to a named tuple.

date.isoformat()¶

Return a string representing the date in ISO 8601 format, YYYY-MM-DD:

>>> from datetime import date
>>> date(2002, 12, 4).isoformat()
'2002-12-04'

date.__str__()¶

For a date d, str(d) is equivalent to d.isoformat().

date.ctime()¶

Return a string representing the date:

>>> from datetime import date
>>> date(2002, 12, 4).ctime()
'Wed Dec  4 00:00:00 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 date.ctime() does not invoke) conforms to the C standard.

date.strftime(format)¶

Return a string representing the date, controlled by an explicit format string. Format codes referring to hours, minutes or seconds will see 0 values. See also strftime() and strptime() Behavior and date.isoformat().

date.__format__(format)¶

Same as date.strftime(). This makes it possible to specify a format string for a date object in formatted string literals and when using str.format(). See also strftime() and strptime() Behavior and date.isoformat().

>>> import time
>>> from datetime import date
>>> today = date.today()
>>> today
datetime.date(2007, 12, 5)
>>> today == date.fromtimestamp(time.time())
True
>>> my_birthday = date(today.year, 6, 24)
>>> if my_birthday < today:
...     my_birthday = my_birthday.replace(year=today.year + 1)
...
>>> my_birthday
datetime.date(2008, 6, 24)
>>> time_to_birthday = abs(my_birthday - today)
>>> time_to_birthday.days
202

>>> from datetime import date
>>> d = date.fromordinal(730920) # 730920th day after 1. 1. 0001
>>> d
datetime.date(2002, 3, 11)

>>> # Methods related to formatting string output
>>> d.isoformat()
'2002-03-11'
>>> d.strftime("%d/%m/%y")
'11/03/02'
>>> d.strftime("%A %d. %B %Y")
'Monday 11. March 2002'
>>> d.ctime()
'Mon Mar 11 00:00:00 2002'
>>> 'The {1} is {0:%d}, the {2} is {0:%B}.'.format(d, "day", "month")
'The day is 11, the month is March.'

>>> # Methods for to extracting 'components' under different calendars
>>> t = d.timetuple()
>>> for i in t:
...     print(i)
2002                # year
3                   # month
11                  # day
0
0
0
0                   # weekday (0 = Monday)
70                  # 70th day in the year
-1
>>> ic = d.isocalendar()
>>> for i in ic:
...     print(i)
2002                # ISO year
11                  # ISO week number
1                   # ISO day number ( 1 = Monday )

>>> # A date object is immutable; all operations produce a new object
>>> d.replace(year=2005)
datetime.date(2005, 3, 11)

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.datetime(year, month, day, hour=0, minute=0, second=0, microsecond=0, tzinfo=None, *, fold=0)¶

The year, month and day arguments are required. tzinfo may be None, or an instance of a tzinfo subclass. 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,

• 0 <= microsecond < 1000000,

• fold in [0, 1].

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

Changed in version 3.6: Added the fold parameter.

Other constructors, all class methods:

classmethod datetime.today()¶

Return the current local date and time, with tzinfo None.

Equivalent to:

datetime.fromtimestamp(time.time())

See also now(), fromtimestamp().

This method is functionally equivalent to now(), but without a tz parameter.

classmethod datetime.now(tz=None)¶

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).

If tz is not None, it must be an instance of a tzinfo subclass, and the current date and time are converted to tz’s time zone.

This function is preferred over today() and utcnow().

Note

Subsequent calls to datetime.now() may return the same instant depending on the precision of the underlying clock.

classmethod datetime.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. An aware current UTC datetime can be obtained by calling datetime.now(timezone.utc). See also now().

Warning

Because naive datetime objects are treated by many datetime methods as local times, it is preferred to use aware datetimes to represent times in UTC. As such, the recommended way to create an object representing the current time in UTC is by calling datetime.now(timezone.utc).

Deprecated since version 3.12: Use datetime.now() with UTC instead.

classmethod datetime.fromtimestamp(timestamp, tz=None)¶

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.

If tz is not None, it must be an instance of a tzinfo subclass, and the timestamp is converted to tz’s time zone.

fromtimestamp() may raise OverflowError, if the timestamp is out of the range of values supported by the platform C localtime() or gmtime() functions, and OSError on localtime() or gmtime() failure. 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. This method is preferred over utcfromtimestamp().

Changed in version 3.3: Raise OverflowError instead of ValueError if the timestamp is out of the range of values supported by the platform C localtime() or gmtime() functions. Raise OSError instead of ValueError on localtime() or gmtime() failure.

Changed in version 3.6: fromtimestamp() may return instances with fold set to 1.

classmethod datetime.utcfromtimestamp(timestamp)¶

Return the UTC datetime corresponding to the POSIX timestamp, with tzinfo None. (The resulting object is naive.)

This may raise OverflowError, if the timestamp is out of the range of values supported by the platform C gmtime() function, and OSError on gmtime() failure. It’s common for this to be restricted to years in 1970 through 2038.

To get an aware datetime object, call fromtimestamp():

datetime.fromtimestamp(timestamp, timezone.utc)

On the POSIX compliant platforms, it is equivalent to the following expression:

datetime(1970, 1, 1, tzinfo=timezone.utc) + timedelta(seconds=timestamp)

except the latter formula always supports the full years range: between MINYEAR and MAXYEAR inclusive.

Warning

Because naive datetime objects are treated by many datetime methods as local times, it is preferred to use aware datetimes to represent times in UTC. As such, the recommended way to create an object representing a specific timestamp in UTC is by calling datetime.fromtimestamp(timestamp, tz=timezone.utc).

Changed in version 3.3: Raise OverflowError instead of ValueError if the timestamp is out of the range of values supported by the platform C gmtime() function. Raise OSError instead of ValueError on gmtime() failure.

Deprecated since version 3.12: Use datetime.fromtimestamp() with UTC instead.

classmethod datetime.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.

classmethod datetime.combine(date, time, tzinfo=time.tzinfo)¶

Return a new datetime object whose date components are equal to the given date object’s, and whose time components are equal to the given time object’s. If the tzinfo argument is provided, its value is used to set the tzinfo attribute of the result, otherwise the tzinfo attribute of the time argument is used. If the date argument is a datetime object, its time components and tzinfo attributes are ignored.

For any datetime object d, d == datetime.combine(d.date(), d.time(), d.tzinfo).

Changed in version 3.6: Added the tzinfo argument.

classmethod datetime.fromisoformat(date_string)¶

Return a datetime corresponding to a date_string in any valid ISO 8601 format, with the following exceptions:

1. Time zone offsets may have fractional seconds.

2. The T separator may be replaced by any single unicode character.

3. Fractional hours and minutes are not supported.

4. Reduced precision dates are not currently supported (YYYY-MM, YYYY).

5. Extended date representations are not currently supported (±YYYYYY-MM-DD).

6. Ordinal dates are not currently supported (YYYY-OOO).

Examples:

>>> from datetime import datetime
>>> datetime.fromisoformat('2011-11-04')
datetime.datetime(2011, 11, 4, 0, 0)
>>> datetime.fromisoformat('20111104')
datetime.datetime(2011, 11, 4, 0, 0)
>>> datetime.fromisoformat('2011-11-04T00:05:23')
datetime.datetime(2011, 11, 4, 0, 5, 23)
>>> datetime.fromisoformat('2011-11-04T00:05:23Z')
datetime.datetime(2011, 11, 4, 0, 5, 23, tzinfo=datetime.timezone.utc)
>>> datetime.fromisoformat('20111104T000523')
datetime.datetime(2011, 11, 4, 0, 5, 23)
>>> datetime.fromisoformat('2011-W01-2T00:05:23.283')
datetime.datetime(2011, 1, 4, 0, 5, 23, 283000)
>>> datetime.fromisoformat('2011-11-04 00:05:23.283')
datetime.datetime(2011, 11, 4, 0, 5, 23, 283000)
>>> datetime.fromisoformat('2011-11-04 00:05:23.283+00:00')
datetime.datetime(2011, 11, 4, 0, 5, 23, 283000, tzinfo=datetime.timezone.utc)
>>> datetime.fromisoformat('2011-11-04T00:05:23+04:00')
datetime.datetime(2011, 11, 4, 0, 5, 23,
    tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))

Added in version 3.7.

Changed in version 3.11: Previously, this method only supported formats that could be emitted by date.isoformat() or datetime.isoformat().

classmethod datetime.fromisocalendar(year, week, day)¶

Return a datetime corresponding to the ISO calendar date specified by year, week and day. The non-date components of the datetime are populated with their normal default values. This is the inverse of the function datetime.isocalendar().

Added in version 3.8.

classmethod datetime.strptime(date_string, format)¶

Return a datetime corresponding to date_string, parsed according to format.

If format does not contain microseconds or time zone information, 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. See also strftime() and strptime() Behavior and datetime.fromisoformat().

Changed in version 3.13: If format specifies a day of month without a year a DeprecationWarning is now emitted. This is to avoid a quadrennial leap year bug in code seeking to parse only a month and day as the default year used in absence of one in the format is not a leap year. Such format values may raise an error as of Python 3.15. The workaround is to always include a year in your format. If parsing date_string values that do not have a year, explicitly add a year that is a leap year before parsing:

>>> from datetime import datetime
>>> date_string = "02/29"
>>> when = datetime.strptime(f"{date_string};1984", "%m/%d;%Y")  # Avoids leap year bug.
>>> when.strftime("%B %d")
'February 29'

Class attributes:

datetime.min¶

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

datetime.max¶

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

datetime.resolution¶

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

Instance attributes (read-only):

datetime.year¶

Between MINYEAR and MAXYEAR inclusive.

datetime.month¶

Between 1 and 12 inclusive.

datetime.day¶

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

datetime.hour¶

In range(24).

datetime.minute¶

In range(60).

datetime.second¶

In range(60).

datetime.microsecond¶

In range(1000000).

datetime.tzinfo¶

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

datetime.fold¶

In [0, 1]. Used to disambiguate wall times during a repeated interval. (A repeated interval occurs when clocks are rolled back at the end of daylight saving time or when the UTC offset for the current zone is decreased for political reasons.) The values 0 and 1 represent, respectively, the earlier and later of the two moments with the same wall time representation.

Added in version 3.6.

Supported operations:

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 attribute 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 attribute as the input datetime, and no time zone adjustments are done even if the input is aware.

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

4. datetime objects are equal if they represent the same date and time, taking into account the time zone.

   Naive and aware datetime objects are never equal.

   If both comparands are aware, and have the same tzinfo attribute, the tzinfo and fold attributes are ignored and the base datetimes are compared. If both comparands are aware and have different tzinfo attributes, the comparison acts as comparands were first converted to UTC datetimes except that the implementation never overflows. datetime instances in a repeated interval are never equal to datetime instances in other time zone.

5. datetime1 is considered less than datetime2 when datetime1 precedes datetime2 in time, taking into account the time zone.

   Order comparison between naive and aware datetime objects raises TypeError.

   If both comparands are aware, and have the same tzinfo attribute, the tzinfo and fold attributes are ignored and the base datetimes are compared. If both comparands are aware and have different tzinfo attributes, the comparison acts as comparands were first converted to UTC datetimes except that the implementation never overflows.

Instance methods:

datetime.date()¶

Return date object with same year, month and day.

datetime.time()¶

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

Changed in version 3.6: The fold value is copied to the returned time object.

datetime.timetz()¶

Return time object with same hour, minute, second, microsecond, fold, and tzinfo attributes. See also method time().

Changed in version 3.6: The fold value is copied to the returned time object.

datetime.replace(year=self.year, month=self.month, day=self.day, hour=self.hour, minute=self.minute, second=self.second, microsecond=self.microsecond, tzinfo=self.tzinfo, *, fold=0)¶

Return a new datetime object with the same attributes, but with specified parameters updated. Note that tzinfo=None can be specified to create a naive datetime from an aware datetime with no conversion of date and time data.

datetime objects are also supported by generic function copy.replace().

Changed in version 3.6: Added the fold parameter.

datetime.astimezone(tz=None)¶

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.

If provided, tz must be an instance of a tzinfo subclass, and its utcoffset() and dst() methods must not return None. If self is naive, it is presumed to represent time in the system time zone.

If called without arguments (or with tz=None) the system local time zone is assumed for the target time zone. The .tzinfo attribute of the converted datetime instance will be set to an instance of timezone with the zone name and offset obtained from the OS.

If self.tzinfo is tz, self.astimezone(tz) is equal to self: no adjustment of date or time data is performed. Else the result is local time in the time zone tz, representing the same UTC time as self: after astz = dt.astimezone(tz), astz - astz.utcoffset() will have the same date and time data as dt - dt.utcoffset().

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).

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 timezone object.
    utc = (self - self.utcoffset()).replace(tzinfo=tz)
    # Convert from UTC to tz's local time.
    return tz.fromutc(utc)

Changed in version 3.3: tz now can be omitted.

Changed in version 3.6: The astimezone() method can now be called on naive instances that are presumed to represent system local time.

datetime.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 with magnitude less than one day.

Changed in version 3.7: The UTC offset is not restricted to a whole number of minutes.

datetime.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 with magnitude less than one day.

Changed in version 3.7: The DST offset is not restricted to a whole number of minutes.

datetime.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,

datetime.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(), yday, dst))

where yday = d.toordinal() - date(d.year, 1, 1).toordinal() + 1 is the day number within the current year starting with 1 for January 1st. 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.

datetime.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 an OverflowError may be raised if d.year was MINYEAR or MAXYEAR and UTC adjustment spills over a year boundary.

Warning

Because naive datetime objects are treated by many datetime methods as local times, it is preferred to use aware datetimes to represent times in UTC; as a result, using datetime.utctimetuple() may give misleading results. If you have a naive datetime representing UTC, use datetime.replace(tzinfo=timezone.utc) to make it aware, at which point you can use datetime.timetuple().

datetime.toordinal()¶

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

datetime.timestamp()¶

Return POSIX timestamp corresponding to the datetime instance. The return value is a float similar to that returned by time.time().

Naive datetime instances are assumed to represent local time and this method relies on the platform C mktime() function to perform the conversion. Since datetime supports wider range of values than mktime() on many platforms, this method may raise OverflowError or OSError for times far in the past or far in the future.

For aware datetime instances, the return value is computed as:

(dt - datetime(1970, 1, 1, tzinfo=timezone.utc)).total_seconds()

Added in version 3.3.

Changed in version 3.6: The timestamp() method uses the fold attribute to disambiguate the times during a repeated interval.

Note

There is no method to obtain the POSIX timestamp directly from a naive datetime instance representing UTC time. If your application uses this convention and your system time zone is not set to UTC, you can obtain the POSIX timestamp by supplying tzinfo=timezone.utc:

timestamp = dt.replace(tzinfo=timezone.utc).timestamp()

or by calculating the timestamp directly:

timestamp = (dt - datetime(1970, 1, 1)) / timedelta(seconds=1)

datetime.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().

datetime.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().

datetime.isocalendar()¶

Return a named tuple with three components: year, week and weekday. The same as self.date().isocalendar().

datetime.isoformat(sep='T', timespec='auto')¶

Return a string representing the date and time in ISO 8601 format:

• YYYY-MM-DDTHH:MM:SS.ffffff, if microsecond is not 0

• YYYY-MM-DDTHH:MM:SS, if microsecond is 0

If utcoffset() does not return None, a string is appended, giving the UTC offset:

• YYYY-MM-DDTHH:MM:SS.ffffff+HH:MM[:SS[.ffffff]], if microsecond is not 0

• YYYY-MM-DDTHH:MM:SS+HH:MM[:SS[.ffffff]], if microsecond is 0

Examples:

>>> from datetime import datetime, timezone
>>> datetime(2019, 5, 18, 15, 17, 8, 132263).isoformat()
'2019-05-18T15:17:08.132263'
>>> datetime(2019, 5, 18, 15, 17, tzinfo=timezone.utc).isoformat()
'2019-05-18T15:17:00+00:00'

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):
...     """A time zone with an arbitrary, constant -06:39 offset."""
...     def utcoffset(self, dt):
...         return timedelta(hours=-6, minutes=-39)
...
>>> datetime(2002, 12, 25, tzinfo=TZ()).isoformat(' ')
'2002-12-25 00:00:00-06:39'
>>> datetime(2009, 11, 27, microsecond=100, tzinfo=TZ()).isoformat()
'2009-11-27T00:00:00.000100-06:39'

The optional argument timespec specifies the number of additional components of the time to include (the default is 'auto'). It can be one of the following:

• 'auto': Same as 'seconds' if microsecond is 0, same as 'microseconds' otherwise.

• 'hours': Include the hour in the two-digit HH format.

• 'minutes': Include hour and minute in HH:MM format.

• 'seconds': Include hour, minute, and second in HH:MM:SS format.

• 'milliseconds': Include full time, but truncate fractional second part to milliseconds. HH:MM:SS.sss format.

• 'microseconds': Include full time in HH:MM:SS.ffffff format.

Note

Excluded time components are truncated, not rounded.

ValueError will be raised on an invalid timespec argument:

>>> from datetime import datetime
>>> datetime.now().isoformat(timespec='minutes')
'2002-12-25T00:00'
>>> dt = datetime(2015, 1, 1, 12, 30, 59, 0)
>>> dt.isoformat(timespec='microseconds')
'2015-01-01T12:30:59.000000'

Changed in version 3.6: Added the timespec parameter.

datetime.__str__()¶

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

datetime.ctime()¶

Return a string representing the date and time:

>>> from datetime import datetime
>>> datetime(2002, 12, 4, 20, 30, 40).ctime()
'Wed Dec  4 20:30:40 2002'

The output string will not include time zone information, regardless of whether the input is aware or naive.

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.

datetime.strftime(format)¶

Return a string representing the date and time, controlled by an explicit format string. See also strftime() and strptime() Behavior and datetime.isoformat().

datetime.__format__(format)¶

Same as datetime.strftime(). This makes it possible to specify a format string for a datetime object in formatted string literals and when using str.format(). See also strftime() and strptime() Behavior and datetime.isoformat().

>>> from datetime import datetime, date, time, timezone

>>> # Using datetime.combine()
>>> d = date(2005, 7, 14)
>>> t = time(12, 30)
>>> datetime.combine(d, t)
datetime.datetime(2005, 7, 14, 12, 30)

>>> # Using datetime.now()
>>> datetime.now()
datetime.datetime(2007, 12, 6, 16, 29, 43, 79043)   # GMT +1
>>> datetime.now(timezone.utc)
datetime.datetime(2007, 12, 6, 15, 29, 43, 79060, tzinfo=datetime.timezone.utc)

>>> # Using datetime.strptime()
>>> dt = datetime.strptime("21/11/06 16:30", "%d/%m/%y %H:%M")
>>> dt
datetime.datetime(2006, 11, 21, 16, 30)

>>> # Using datetime.timetuple() to get tuple of all attributes
>>> tt = dt.timetuple()
>>> for it in tt:
...     print(it)
...
2006    # year
11      # month
21      # day
16      # hour
30      # minute
0       # second
1       # weekday (0 = Monday)
325     # number of days since 1st January
-1      # dst - method tzinfo.dst() returned None

>>> # Date in ISO format
>>> ic = dt.isocalendar()
>>> for it in ic:
...     print(it)
...
2006    # ISO year
47      # ISO week
2       # ISO weekday

>>> # Formatting a datetime
>>> dt.strftime("%A, %d. %B %Y %I:%M%p")
'Tuesday, 21. November 2006 04:30PM'
>>> 'The {1} is {0:%d}, the {2} is {0:%B}, the {3} is {0:%I:%M%p}.'.format(dt, "day", "month", "time")
'The day is 21, the month is November, the time is 04:30PM.'

from datetime import timedelta, datetime, tzinfo, timezone

class KabulTz(tzinfo):
    # Kabul used +4 until 1945, when they moved to +4:30
    UTC_MOVE_DATE = datetime(1944, 12, 31, 20, tzinfo=timezone.utc)

    def utcoffset(self, dt):
        if dt.year < 1945:
            return timedelta(hours=4)
        elif (1945, 1, 1, 0, 0) <= dt.timetuple()[:5] < (1945, 1, 1, 0, 30):
            # An ambiguous ("imaginary") half-hour range representing
            # a 'fold' in time due to the shift from +4 to +4:30.
            # If dt falls in the imaginary range, use fold to decide how
            # to resolve. See PEP495.
            return timedelta(hours=4, minutes=(30 if dt.fold else 0))
        else:
            return timedelta(hours=4, minutes=30)

    def fromutc(self, dt):
        # Follow same validations as in datetime.tzinfo
        if not isinstance(dt, datetime):
            raise TypeError("fromutc() requires a datetime argument")
        if dt.tzinfo is not self:
            raise ValueError("dt.tzinfo is not self")

        # A custom implementation is required for fromutc as
        # the input to this function is a datetime with utc values
        # but with a tzinfo set to self.
        # See datetime.astimezone or fromtimestamp.
        if dt.replace(tzinfo=timezone.utc) >= self.UTC_MOVE_DATE:
            return dt + timedelta(hours=4, minutes=30)
        else:
            return dt + timedelta(hours=4)

    def dst(self, dt):
        # Kabul does not observe daylight saving time.
        return timedelta(0)

    def tzname(self, dt):
        if dt >= self.UTC_MOVE_DATE:
            return "+04:30"
        return "+04"

>>> tz1 = KabulTz()

>>> # Datetime before the change
>>> dt1 = datetime(1900, 11, 21, 16, 30, tzinfo=tz1)
>>> print(dt1.utcoffset())
4:00:00

>>> # Datetime after the change
>>> dt2 = datetime(2006, 6, 14, 13, 0, tzinfo=tz1)
>>> print(dt2.utcoffset())
4:30:00

>>> # Convert datetime to another time zone
>>> dt3 = dt2.astimezone(timezone.utc)
>>> dt3
datetime.datetime(2006, 6, 14, 8, 30, tzinfo=datetime.timezone.utc)
>>> dt2
datetime.datetime(2006, 6, 14, 13, 0, tzinfo=KabulTz())
>>> dt2 == dt3
True

time Objects¶

A time object represents a (local) time of day, independent of any particular day, and subject to adjustment via a tzinfo object.

class datetime.time(hour=0, minute=0, second=0, microsecond=0, tzinfo=None, *, fold=0)¶

All arguments are optional. tzinfo may be None, or an instance of a tzinfo subclass. The remaining arguments must be integers in the following ranges:

• 0 <= hour < 24,

• 0 <= minute < 60,

• 0 <= second < 60,

• 0 <= microsecond < 1000000,

• fold in [0, 1].

If an argument outside those ranges is given, ValueError is raised. All default to 0 except tzinfo, which defaults to None.

Class attributes:

time.min¶

The earliest representable time, time(0, 0, 0, 0).

time.max¶

The latest representable time, time(23, 59, 59, 999999).

time.resolution¶

The smallest possible difference between non-equal time objects, timedelta(microseconds=1), although note that arithmetic on time objects is not supported.

Instance attributes (read-only):

time.hour¶

In range(24).

time.minute¶

In range(60).

time.second¶

In range(60).

time.microsecond¶

In range(1000000).

time.tzinfo¶

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

time.fold¶

In [0, 1]. Used to disambiguate wall times during a repeated interval. (A repeated interval occurs when clocks are rolled back at the end of daylight saving time or when the UTC offset for the current zone is decreased for political reasons.) The values 0 and 1 represent, respectively, the earlier and later of the two moments with the same wall time representation.

Added in version 3.6.

time objects support equality and order comparisons, where a is considered less than b when a precedes b in time.

Naive and aware time objects are never equal. Order comparison between naive and aware time objects raises TypeError.

If both comparands are aware, and have the same tzinfo attribute, the tzinfo and fold attributes are ignored and the base times are compared. If both comparands are aware and have different tzinfo attributes, the comparands are first adjusted by subtracting their UTC offsets (obtained from self.utcoffset()).

In Boolean contexts, a time object is always considered to be true.

Other constructor:

classmethod time.fromisoformat(time_string)¶

Return a time corresponding to a time_string in any valid ISO 8601 format, with the following exceptions:

1. Time zone offsets may have fractional seconds.

2. The leading T, normally required in cases where there may be ambiguity between a date and a time, is not required.

3. Fractional seconds may have any number of digits (anything beyond 6 will be truncated).

4. Fractional hours and minutes are not supported.

Examples:

>>> from datetime import time
>>> time.fromisoformat('04:23:01')
datetime.time(4, 23, 1)
>>> time.fromisoformat('T04:23:01')
datetime.time(4, 23, 1)
>>> time.fromisoformat('T042301')
datetime.time(4, 23, 1)
>>> time.fromisoformat('04:23:01.000384')
datetime.time(4, 23, 1, 384)
>>> time.fromisoformat('04:23:01,000384')
datetime.time(4, 23, 1, 384)
>>> time.fromisoformat('04:23:01+04:00')
datetime.time(4, 23, 1, tzinfo=datetime.timezone(datetime.timedelta(seconds=14400)))
>>> time.fromisoformat('04:23:01Z')
datetime.time(4, 23, 1, tzinfo=datetime.timezone.utc)
>>> time.fromisoformat('04:23:01+00:00')
datetime.time(4, 23, 1, tzinfo=datetime.timezone.utc)

Added in version 3.7.

Changed in version 3.11: Previously, this method only supported formats that could be emitted by time.isoformat().

Instance methods:

time.replace(hour=self.hour, minute=self.minute, second=self.second, microsecond=self.microsecond, tzinfo=self.tzinfo, *, fold=0)¶

Return a new time with the same values, but with specified parameters updated. Note that tzinfo=None can be specified to create a naive time from an aware time, without conversion of the time data.

time objects are also supported by generic function copy.replace().

Changed in version 3.6: Added the fold parameter.

time.isoformat(timespec='auto')¶

Return a string representing the time in ISO 8601 format, one of:

• HH:MM:SS.ffffff, if microsecond is not 0

• HH:MM:SS, if microsecond is 0

• HH:MM:SS.ffffff+HH:MM[:SS[.ffffff]], if utcoffset() does not return None

• HH:MM:SS+HH:MM[:SS[.ffffff]], if microsecond is 0 and utcoffset() does not return None

The optional argument timespec specifies the number of additional components of the time to include (the default is 'auto'). It can be one of the following:

• 'auto': Same as 'seconds' if microsecond is 0, same as 'microseconds' otherwise.

• 'hours': Include the hour in the two-digit HH format.

• 'minutes': Include hour and minute in HH:MM format.

• 'seconds': Include hour, minute, and second in HH:MM:SS format.

• 'milliseconds': Include full time, but truncate fractional second part to milliseconds. HH:MM:SS.sss format.

• 'microseconds': Include full time in HH:MM:SS.ffffff format.

Note

Excluded time components are truncated, not rounded.

ValueError will be raised on an invalid timespec argument.

Example:

>>> from datetime import time
>>> time(hour=12, minute=34, second=56, microsecond=123456).isoformat(timespec='minutes')
'12:34'
>>> dt = time(hour=12, minute=34, second=56, microsecond=0)
>>> dt.isoformat(timespec='microseconds')
'12:34:56.000000'
>>> dt.isoformat(timespec='auto')
'12:34:56'

Changed in version 3.6: Added the timespec parameter.

time.__str__()¶

For a time t, str(t) is equivalent to t.isoformat().

time.strftime(format)¶

Return a string representing the time, controlled by an explicit format string. See also strftime() and strptime() Behavior and time.isoformat().

time.__format__(format)¶

Same as time.strftime(). This makes it possible to specify a format string for a time object in formatted string literals and when using str.format(). See also strftime() and strptime() Behavior and time.isoformat().

time.utcoffset()¶

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

Changed in version 3.7: The UTC offset is not restricted to a whole number of minutes.

time.dst()¶

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

Changed in version 3.7: The DST offset is not restricted to a whole number of minutes.

time.tzname()¶

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

>>> from datetime import time, tzinfo, timedelta
>>> class TZ1(tzinfo):
...     def utcoffset(self, dt):
...         return timedelta(hours=1)
...     def dst(self, dt):
...         return timedelta(0)
...     def tzname(self,dt):
...         return "+01:00"
...     def  __repr__(self):
...         return f"{self.__class__.__name__}()"
...
>>> t = time(12, 10, 30, tzinfo=TZ1())
>>> t
datetime.time(12, 10, 30, tzinfo=TZ1())
>>> t.isoformat()
'12:10:30+01:00'
>>> t.dst()
datetime.timedelta(0)
>>> t.tzname()
'+01:00'
>>> t.strftime("%H:%M:%S %Z")
'12:10:30 +01:00'
>>> 'The {} is {:%H:%M}.'.format("time", t)
'The time is 12:10.'

tzinfo Objects¶

class datetime.tzinfo¶

This is an abstract base class, meaning that this class should not be instantiated directly. Define a subclass of tzinfo to capture information about a particular time zone.

An instance of (a concrete subclass of) tzinfo can be passed to the constructors for datetime and time objects. The latter objects view their attributes as being in local time, and the tzinfo object supports methods revealing offset of local time from UTC, the name of the time zone, and DST offset, all relative to a date or time object passed to them.

You need to derive a concrete subclass, and (at least) supply implementations of the standard tzinfo methods needed by the datetime methods you use. The datetime module provides timezone, a simple concrete subclass of tzinfo which can represent time zones with fixed offset from UTC such as UTC itself or North American EST and EDT.

Special requirement for pickling: A tzinfo subclass must have an __init__() method that can be called with no arguments, otherwise it can be pickled but possibly not unpickled again. This is a technical requirement that may be relaxed in the future.

A concrete subclass of tzinfo may need to implement 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.

tzinfo.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 tzinfo object represents both time zone and DST adjustments, 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 utcoffset() will probably look like one of these two:

return CONSTANT                 # fixed-offset class
return CONSTANT + self.dst(dt)  # daylight-aware class

If utcoffset() does not return None, dst() should not return None either.

The default implementation of utcoffset() raises NotImplementedError.

Changed in version 3.7: The UTC offset is not restricted to a whole number of minutes.

tzinfo.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 utcoffset() for details). Note that DST offset, if applicable, has already been added to the UTC offset returned by utcoffset(), so there’s no need to consult dst() unless you’re interested in obtaining DST info separately. For example, datetime.timetuple() calls its tzinfo attribute’s dst() method to determine how the tm_isdst flag should be set, and tzinfo.fromutc() calls dst() to account for DST changes when crossing time zones.

An instance tz of a tzinfo subclass that models both standard and daylight times must be consistent in this sense:

tz.utcoffset(dt) - tz.dst(dt)

must return the same result for every datetime dt with dt.tzinfo == tz. For sane tzinfo subclasses, this expression yields the time zone’s “standard offset”, which should not depend on the date or the time, but only on geographic location. The implementation of datetime.astimezone() relies on this, but cannot detect violations; it’s the programmer’s responsibility to ensure it. If a tzinfo subclass cannot guarantee this, it may be able to override the default implementation of tzinfo.fromutc() to work correctly with astimezone() regardless.

Most implementations of 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.year, and expressed
    # in standard local time.

    if dston <= dt.replace(tzinfo=None) < dstoff:
        return timedelta(hours=1)
    else:
        return timedelta(0)

The default implementation of dst() raises NotImplementedError.

Changed in version 3.7: The DST offset is not restricted to a whole number of minutes.

tzinfo.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 tzinfo subclasses will wish to return different names depending on the specific value of dt passed, especially if the tzinfo class is accounting for daylight time.

The default implementation of tzname() raises NotImplementedError.

These methods are called by a datetime or time object, in response to their methods of the same names. A datetime object passes itself as the argument, and a time object passes None as the argument. A tzinfo subclass’s methods should therefore be prepared to accept a dt argument of None, or of class