Django model fields for easily creating fields with min and max validators and that renders with min and max attributes on the input element.

bounded-fields.py

from typing import Dict, Optional, Any

from django.db import models
from django.core.validators import MinValueValidator, MaxValueValidator
from django import forms


class BaseBoundedField(models.Field):
    def __init__(
            self,
            min_value: float = float('-infinity'),
            max_value: float = float('infinity'),
            step: Optional[float] = None,
            *args: Any, **kwargs: Any):
        self.max_value = max_value
        self.min_value = min_value
        self.step = step
        kwargs['validators'] = list(kwargs.get('validators', [])) + [
            MinValueValidator(self.min_value),
            MaxValueValidator(self.max_value)]
        super().__init__(*args, **kwargs)

    def _get_widget_attrs(self) -> Dict[str, str]:
        attrs = {}
        if self.max_value < float('infinity'):
            attrs['max'] = str(self.max_value)
        if self.min_value > float('-infinity'):
            attrs['min'] = str(self.min_value)
        if self.step is not None:
            attrs['step'] = str(self.step)
        return attrs


class BoundedFloatField(BaseBoundedField, models.FloatField):
    def formfield(self, **kwargs: Any) -> forms.Field:
        defaults = {
            'widget': forms.NumberInput(attrs=self._get_widget_attrs()),
        }
        defaults.update(kwargs)
        return super().formfield(**defaults)


class BoundedIntegerField(BaseBoundedField, models.IntegerField):
    def formfield(self, **kwargs: Any) -> forms.Field:
        defaults = {
            'widget': forms.NumberInput(attrs=self._get_widget_attrs()),
        }
        defaults.update(kwargs)
        return super().formfield(**defaults)