django源码解析之 BooleanField (二)

class BooleanField(Field):
    empty_strings_allowed = False
    default_error_messages = {
        'invalid': _(u"'%s' value must be either True or False."),
    }
    description = _("Boolean (Either True or False)")

    def __init__(self, *args, **kwargs):
        kwargs['blank'] = True
        if 'default' not in kwargs and not kwargs.get('null'):
            kwargs['default'] = False
        Field.__init__(self, *args, **kwargs)

    def get_internal_type(self):
        return "BooleanField"

    def to_python(self, value):
        if value in (True, False):
            # if value is 1 or 0 than it's equal to True or False, but we want
            # to return a true bool for semantic reasons.
            return bool(value)
        if value in ('t', 'True', ''):
            return True
        if value in ('f', 'False', ''):
            return False
        msg = self.error_messages['invalid'] % str(value)
        raise exceptions.ValidationError(msg)

    def get_prep_lookup(self, lookup_type, value):
        # Special-case handling for filters coming from a Web request (e.g. the
        # admin interface). Only works for scalar values (not lists). If you're
        # passing in a list, you might as well make things the right type when
        # constructing the list.
        if value in ('', ''):
            value = bool(int(value))
        return super(BooleanField, self).get_prep_lookup(lookup_type, value)

    def get_prep_value(self, value):
        if value is None:
            return None
        return bool(value)

    def formfield(self, **kwargs):
        # Unlike most fields, BooleanField figures out include_blank from
        # self.null instead of self.blank.
        if self.choices:
            include_blank = (self.null or
                             not (self.has_default() or 'initial' in kwargs))
            defaults = {'choices': self.get_choices(
                                       include_blank=include_blank)}
        else:
            defaults = {'form_class': forms.BooleanField}
        defaults.update(kwargs)
        return super(BooleanField, self).formfield(**defaults)

看起来，BooleanField 要比复杂的多，我们只分析其中的

to_python 函数

     def to_python(self, value):
         if value in (True, False):
             # if value is 1 or 0 than it's equal to True or False, but we want
             # to return a true bool for semantic reasons.
             return bool(value)
         if value in ('t', 'True', ''):
             return True
         if value in ('f', 'False', ''):
             return False
         msg = self.error_messages['invalid'] % str(value)
         raise exceptions.ValidationError(msg)

函数获得一个参数value，判断value是不是 （True，False，1, 0）中的一个，如果是，返回True或False。

下面同理，在value是字符串的情况下，判断value的值  是不是 ('t', 'True', '1') 中的一个，是则返回 True...

如果执行到msg = XXXXX 这里，就说明 to_python执行失败了，返回错误...抛出异常...

---

需要注意的是：

>>> a = True
>>> b = False
>>> c = 1
>>> d = 0
>>> e = 11
>>> f = -1
>>> a in (True,False)
True
>>> b in (True,False)
True
>>> c in (True,False)
True
>>> d in (True,False)
True
>>> e in (True,False)
False
>>> f in (True,False)
False
>>> 

如果一个大于1的数，是不会 in (True,False) 中的，这和我们平时使用

>>> if 11:
    print 'aa'

aa
>>> 

是不同的。