CODEWITHSUNDEEP
pythondatedictionarykey
daGrevis
daGrevis

Reputation: 21333

Date object with year and month only

Is it possible to create date object with year and month only? I don't need day.

In [5]: from datetime import date

In [6]: date(year=2013, month=1)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-6-a84d4034b10c> in <module>()
----> 1 date(year=2013, month=1)

TypeError: Required argument 'day' (pos 3) not found

I'm using the date object as key in my dictionary and January 20 must have the same key as January 21, because they are in same month and year.

I used a simple integer before that as a month number. Unfortunately I need to know the year too!

Upvotes: 37

Views: 58185

Answers (5)

Kevin Kleinfelter
Kevin Kleinfelter

Reputation: 575

This implements a class which is just like datetime.date, but you need not specify the day. i.e. It allows you to "create date object with year and month only."

class Mdate(datetime.date):
    """ A datetime.date where day doesn't matter. """

    def __new__(cls, year, month):
        """Python calls __new__ instead of __init__ for immutable objects."""
        return super().__new__(cls, year, month, 1)

    def __repr__(self):
        """Because you're implementing __new__ you also need __repr__ or else you get
        TypeError: __new__() takes 3 positional arguments but 4 were given."""
        return '{0}({1}, {2}, 1)'.format(self.__class__.__name__, self.year, self.month)

    def __reduce__(self):
        """You need __reduce__ to support pickling."""
        return (self.__class__, (self.year, self.month))

I have a boatload of code where the day of month is irrelevant, and removing the day from the date constructor clarifies that code.

Sample use:

d = Mdate(2020, 12)

Upvotes: 1

Haimei
Haimei

Reputation: 12975

If you want to use datetime, you must follow its attributes. Here I quote it from the official website:

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

So, you can't ignore day and remember to give assignment.

Upvotes: 4

zeroclyy
zeroclyy

Reputation: 85

import datetime

date = datetime.date(year=2013, month=1, day=4)
str(date.year) + '-' + str(date.month)

Upvotes: 6

reader_1000
reader_1000

Reputation: 2501

As an addition to other answer, you can use namedtuple.

from collections import namedtuple
MyDate = namedtuple('MyDate', ['month', 'year'])
dkey = MyDate(year=2013, month=1)

Upvotes: 20

Martijn Pieters
Martijn Pieters

Reputation: 1123042

No, you can't do that. For your usecase, use a tuple instead:

key = (2013, 1)

Since you don't need to do date manipulations on the value a tuple more than suffices.

Upvotes: 26

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