Django模型 - 导入问题

Question

我把我的模型文件整理成了一个模块，这样维护代码就容易多了，因为代码量已经增长得很大了。

有趣的是，其中有一个类引用了另一个类，而那个类又反过来引用了第一个类，这样就出现了问题：

更新：这种循环引用让Python感到困惑，这就是问题的根源。当你只在模型定义中引用其他模型时，这个问题很容易解决。然而，Picture类有一些方法引用了paperType类，反过来也一样——这个问题该怎么解决呢？

这是Picture类的代码：

from django.db import models
from django.utils import simplejson
from picviewer.models import Collection, ImageSizeRatio, printSize

class Picture(models.Model):
    name = models.TextField(null=False,blank=False,unique=False)
    collection = models.ForeignKey(Collection)
    popularity = models.IntegerField(default=0,unique=False)
    isPurchasable = models.BooleanField(default=False)
    allowBuyExclusive = models.BooleanField(default=False)
    basePrice = models.DecimalField(decimal_places=2,max_digits=8)
    imageSizeRatio = models.ForeignKey(ImageSizeRatio)
    imageThumbnail = models.FileField(upload_to='pictures')
    imagePreview = models.FileField(upload_to='pictures')
    imageSmall = models.FileField(upload_to='pictures')
    imageNormal = models.FileField(upload_to='pictures')
    imageLarge = models.FileField(upload_to='pictures')
    imageHuge = models.FileField(upload_to='pictures')
    allowedPrintSize = models.ManyToManyField(printSize)

这是它引用的printSize类，你可以看到它调用了Picture的一些函数来处理指定printSize的图片：

from django.db import models
from picviewer.models import paperType
from picviewer.models import Picture

class printSize (models.Model):
    name = models.CharField(null=False,blank=False,unique=True,max_length=60)
    width = models.IntegerField(null=False,blank=False)
    height = models.IntegerField(null=False,blank=False)
    allowedPaperType = models.ManyToManyField(paperType)
    #isActive = models.NullBooleanField(null=True, default=None)

    def json(self, picture_id, base_price):
        sizes_selector = printSize.objects.filter(picture__id = picture_id)
        sizes = list()
        for size in sizes_selector:
            papers = list()
            for paper in size.allowedPaperType.all():
                cost_for_paper = Picture.objects.get(id=picture_id).calculatePrice(paper.id,size.id)
                p = dict(id = paper.id,
                         name = paper.name,
                         description = paper.description,
                         price = paper.pricePerSqMeter.__str__(),
                         cost = "%.2f" % cost_for_paper)
                papers.append(p)
            s = dict(id = size.id,
                     name = size.name,
                     width = size.width,
                     height = size.height,
                     allowedPapers = papers)
            sizes.append(s)
        return sizes

现在我在尝试导入Picture时，在命令行中得到了这个错误：

>>> from picviewer.models import Picture
Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "D:\~Sasha\eclipse_workspace\zavalen\picviewer\models\Picture.py", line 4, in <module>
    from picviewer.models import Collection, ImageSizeRatio, printSize
  File "D:\~Sasha\eclipse_workspace\zavalen\picviewer\models\printSize.py", line 4, in <module>
    from picviewer.models import Picture
ImportError: cannot import name Picture
>>>

我能解决这个问题吗？ :)

django 代码维护模型设计方法调用类引用导入错误依赖关系循环引用

Django模型 - 导入问题

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