A MonthField for the peewee ORM. Inspired by https://github.com/clearspark/django-monthfield.

peewee_monthfield.py

from peewee import _BaseFormattedField, format_date_time, _date_part
import datetime


class MonthField(_BaseFormattedField):
    field_type = 'DATE'
    formats = [
        '%Y-%m',
        '%Y-%m-%d',
        '%Y-%m-%d %H:%M:%S',
        '%Y-%m-%d %H:%M:%S.%f',
    ]

    def db_value(self, value):
        " Store datetime.date object of first day in db. "
        month = self.python_value(value)
        if month is not None:
            return month.first_day()
        return None

    def python_value(self, value):
        " Return Month object for given value. "
        if value and isinstance(value, Month):
            return value
        elif value and isinstance(value, str):
            return format_date_time(value, self.formats, Month.from_date)
        elif value and isinstance(value, (datetime.datetime, datetime.date)):
            return Month.from_date(value)
        return None

    def to_timestamp(self):
        return self.model._meta.database.to_timestamp(self)

    def truncate(self, part):
        return self.model._meta.database.truncate_date(part, self)

    year = property(_date_part('year'))
    month = property(_date_part('month'))


"""
Month borrowed from https://github.com/clearspark/django-monthfield/ with modification.

Copyright (c) 2019, clearSpark
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice, this
  list of conditions and the following disclaimer.

* Redistributions in binary form must reproduce the above copyright notice,
  this list of conditions and the following disclaimer in the documentation
  and/or other materials provided with the distribution.

* Neither the name of django-monthfield nor the names of its
  contributors may be used to endorse or promote products derived from
  this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
"""

def days(days):
    return datetime.timedelta(days=days)


class Month():
    def __init__(self, year, month):
        self.year = year
        self.month = month
        self._date = datetime.date(year=self.year, month=self.month, day=1)

    @classmethod
    def from_int(cls, months):
        y, m = divmod(months, 12)
        m += 1
        return cls(y, m)

    @classmethod
    def from_date(cls, date):
        return cls(date.year, date.month)

    @classmethod
    def from_string(cls, date):
        y = int(date[:4])
        m = int(date[5:7])
        return cls(y, m)

    def __add__(self, x):
        '''x is an integer'''
        return Month.from_int(int(self) + x)

    def __sub__(self, x):
        '''x is integer or Month instance'''
        if isinstance(x, Month):
            return int(self) - int(x)
        else:
            return Month.from_int(int(self) - int(x))

    def next_month(self):
        return self + 1

    def prev_month(self):
        return self - 1

    def first_day(self):
        return self._date

    def last_day(self):
        return self.next_month().first_day() - days(1)

    def __int__(self):
        return self.year * 12 + self.month - 1

    def __contains__(self, date):
        return self == date

    def __eq__(self, x):
        if isinstance(x, Month):
            return x.month == self.month and x.year == self.year
        if isinstance(x, datetime.date):
            return self.year == x.year and self.month == x.month
        if isinstance(x, int):
            return x == int(self)
        if isinstance(x, str):
            return str(self) == x[:7]

    def __gt__(self, x):
        if isinstance(x, Month):
            if self.year != x.year: return self.year > x.year
            return self.month > x.month
        if isinstance(x, datetime.date):
            return self.first_day() > x
        if isinstance(x, int):
            return int(self) > x
        if isinstance(x, str):
            return str(self) > x[:7]

    def __ne__(self, x):
        return not self == x

    def __le__(self, x):
        return not self > x

    def __ge__(self, x):
        return (self > x) or (self == x)

    def __lt__(self, x):
        return not self >= x

    def __str__(self):
        return '%s-%02d' %(self.year, self.month)

    def __repr__(self):
        return self.__str__()

    def __hash__(self):
        return hash(self.datestring())

    def datestring(self):
        return self.first_day().isoformat()

    isoformat = datestring

    def range(self, x):
        '''x must be an instance of Month that is larger than self.
        returns a list of Month objects that make up the timespan from self to x (inclusive)'''
        months_as_ints = range(int(self), int(x) + 1)
        return [ Month.from_int(i) for i in months_as_ints ]

    def strftime(self, fmt):
        return self._date.strftime(fmt)

test_monthfield.py

import unittest
import peewee
import datetime
from peewee_monthfield import MonthField, Month


db = peewee.SqliteDatabase(':memory:')


class TestModel(peewee.Model):
    month = MonthField()

    class Meta:
        database = db

class TestMonthField(unittest.TestCase):
    database = db
    requires = [TestModel]

    def setUp(self):
        if not self.database.is_closed():
            self.database.close()
        self.database.connect()
        self.database.create_tables(self.requires)

    def tearDown(self):
        if not self.database.is_closed():
            self.database.rollback()
        try:
            self.database.drop_tables(self.requires, safe=True)
        finally:
            self.database.close()

    def test_model(self):
        TestModel.create(month='2021-09')
        TestModel.create(month=datetime.date(2021, 10, 1))
        TestModel.create(month=Month(2021, 11))

        s = TestModel.get(TestModel.month == datetime.date(2021, 9, 1))
        self.assertIsInstance(s.month, Month)
        self.assertEqual(s.month, Month(2021, 9))

        o = TestModel.get(TestModel.month == Month(2021, 10))
        self.assertIsInstance(o.month, Month)
        self.assertEqual(o.month, Month(2021, 10))

        n = TestModel.get(TestModel.month == '2021-11')
        self.assertIsInstance(n.month, Month)
        self.assertEqual(n.month, Month(2021, 11))


if __name__ == '__main__':
    unittest.main()