datetime — Basic date and time types

Source code: Lib/datetime.py


The datetime module supplies classes for manipulating dates and times.

While date and time arithmetic is supported, the focus of the implementation is on efficient attribute extraction for output formatting and manipulation.

{tip}
Module calendar

General calendar related functions.

Module time

Time access and conversions.

Package dateutil

Third-party library with expanded time zone and parsing support.

Aware and Naive Objects

Date and time objects may be categorized as “aware” or “naive” depending on whether or not they include timezone 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 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 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 timezones with fixed offsets from UTC, such as UTC itself or North American EST and EDT timezones. Supporting timezones 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.

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 date, time, or datetime 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.

New in version 3.2.

Objects of these types are immutable.

Subclass relationships:

object
    timedelta
    tzinfo
        timezone
    time
    date
        datetime

Common Properties

The date, datetime, time, and timezone types share these common features:

  • Objects of these types are immutable.

  • Objects of these types are hashable, meaning that they can be used as dictionary keys.

  • Objects of these types support efficient pickling via the pickle module.

Determining if an Object is Aware or Naive

Objects of the date type are always naive.

An object of type time or datetime may be aware or naive.

A datetime object d is aware if both of the following hold:

  1. d.tzinfo is not None

  2. d.tzinfo.utcoffset(d) does not return None

Otherwise, d is naive.

A time object t is aware if both of the following hold:

  1. t.tzinfo is not None

  2. t.tzinfo.utcoffset(None) does not return None.

Otherwise, t is naive.

The distinction between aware and naive doesn’t apply to timedelta objects.

timedelta Objects

A timedelta object represents a duration, the difference between two dates or times.

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)

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 > -timedelta.min. -timedelta.max is not representable as a timedelta object.

Instance attributes (read-only):

Attribute

Value

days

Between -999999999 and 999999999 inclusive

seconds

Between 0 and 86399 inclusive

microseconds

Between 0 and 999999 inclusive

Supported operations:

Operation

Result

t1 = t2 + t3

Sum of t2 and t3. Afterwards t1-t2 == t3 and t1-t3 == t2 are true. (1)

t1 = t2 - t3

Difference of t2 and t3. Afterwards t1 == t2 - t3 and t2 == t1 + t3 are true. (1)(6)

t1 = t2 * i or t1 = i * t2

Delta multiplied by an integer. Afterwards t1 // i == t2 is true, provided i != 0.

In general, t1 * i == t1 * (i-1) + t1 is true. (1)

t1 = t2 * f or t1 = f * t2

Delta multiplied by a float. The result is rounded to the nearest multiple of timedelta.resolution using round-half-to-even.

f = t2 / t3

Division (3) of overall duration t2 by interval unit t3. Returns a float object.

t1 = t2 / f or t1 = t2 / i

Delta divided by a float or an int. The result is rounded to the nearest multiple of timedelta.resolution using round-half-to-even.

t1 = t2 // i or t1 = t2 // t3

The floor is computed and the remainder (if any) is thrown away. In the second case, an integer is returned. (3)

t1 = t2 % t3

The remainder is computed as a timedelta object. (3)

q, r = divmod(t1, t2)

Computes the quotient and the remainder: q = t1 // t2 (3) and r = t1 % t2. q is an integer and r is a timedelta object.

+t1

Returns a timedelta object with the same value. (2)

-t1

equivalent to timedelta(-t1.days, -t1.seconds, -t1.microseconds), and to t1* -1. (1)(4)

abs(t)

equivalent to +t when t.days >= 0, and to -t when t.days < 0. (2)

str(t)

Returns a string in the form [D day[s], ][H]H:MM:SS[.UUUUUU], where D is negative for negative t. (5)

repr(t)

Returns a string representation of the timedelta object as a constructor call with canonical attribute values.

Notes:

  1. This is exact but may overflow.

  2. This is exact and cannot overflow.

  3. Division by 0 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).

Changed in version 3.2: Floor division and true division of a timedelta object by another timedelta object are now supported, as are remainder operations and the divmod() function. True division and multiplication of a timedelta object by a float object are now supported.

Comparisons of timedelta objects are supported, with some caveats.

The comparisons == or != always return a bool, no matter the type of the compared object:

>>> from datetime import timedelta
>>> delta1 = timedelta(seconds=57)
>>> delta2 = timedelta(hours=25, seconds=2)
>>> delta2 != delta1
True
>>> delta2 == 5
False

For all other comparisons (such as < and >), when a timedelta object is compared to an object of a different type, TypeError is raised:

>>> delta2 > delta1
True
>>> delta2 > 5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '>' not supported between instances of 'datetime.timedelta' and 'int'

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.

New in version 3.2.

Examples of usage: timedelta

An additional example of normalization:

>>> # 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

Examples of timedelta arithmetic:

>>> 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 the format YYYY-MM-DD:

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

This is the inverse of date.isoformat(). It only supports the format YYYY-MM-DD.

New in version 3.7.

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().

New 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).