Class BooleanField

django/db/models/fields/__init__.py:1200–1243

class BooleanField(Field):
    empty_strings_allowed = False
    default_error_messages = {
        "invalid": _("“%(value)s” value must be either True or False."),
        "invalid_nullable": _("“%(value)s” value must be either True, False, or None."),
    }
    description = _("Boolean (Either True or False)")

    def get_internal_type(self):
        return "BooleanField"

    def to_python(self, value):
        if self.null and value in self.empty_values:
            return None
        if value in (True, False):
            # 1/0 are equal to True/False. bool() converts former to latter.
            return bool(value)
        if value in ("t", "True", "1"):
            return True
        if value in ("f", "False", "0"):
            return False
        raise exceptions.ValidationError(
            self.error_messages["invalid_nullable" if self.null else "invalid"],
            code="invalid",
            params={"value": value},
        )

    def get_prep_value(self, value):
        value = super().get_prep_value(value)
        if value is None:
            return None
        return self.to_python(value)

    def formfield(self, **kwargs):
        if self.choices is not None:
            include_blank = not (self.has_default() or "initial" in kwargs)
            defaults = {"choices": self.get_choices(include_blank=include_blank)}
        else:
            form_class = forms.NullBooleanField if self.null else forms.BooleanField
            # In HTML checkboxes, 'required' means "must be checked" which is
            # different from the choices case ("must select some value").
            # required=False allows unchecked checkboxes.
            defaults = {"form_class": form_class, "required": False}
        return super().formfield(**{**defaults, **kwargs})


class CharField(Field):