python - Django/Python : CSV for-in loop overriding first row each time through

Question

class CSVDownload(View):
    """ Prepares CSV file version to download """       

        #more code here

        f = StringIO.StringIO()
        writer = csv.writer(f, dialect='excel')
        for v in visit_list:
            writer.writerow([v.idfa.idfa, v.name, v.duration, v.firstSeen, v.lastSeen, v.identifier, v.closestProximity])
        f.seek(0)
        response = HttpResponse(f, content_type='text/csv')
        response['Content-Disposition'] = 'attachment; filename=AdvertiserData.csv'

        return response

由于某种原因，在excel中打开文件时，文件只会输出列表中的最后一项，参见

这让我相信每一行都会覆盖第一行。尽管情况不应该如此。看看我在终端中执行的这些测试。

>>> f.getvalue()
'FFAC6F6C-1B2E-47C2-8110-5E619B239FB1,PPTest1,00:00:24,2014-11-11 23:20:24.730000,2014-11-11 23:20:48.750000,nkfe-cnb7s,NEAR\r\nFFAC6F6C-1B2E-47C2-8110-5E619B239FB1,moo2,00:00:24,2014-11-11 23:20:24.730000,2014-11-11 23:20:48.750000,nkfe-cnb7s,NEAR\r\n'

这将返回多个值，值之间有 \r\n。

另外，我也尝试过

>>> print response
Content-Type: text/csv
Content-Disposition: attachment; filename=boo.csv

FFAC6F6C-1B2E-47C2-8110-5E619B239FB1,PPTest1,00:00:24,2014-11-11 23:20:24.730000,2014-11-11 23:20:48.750000,nkfe-cnb7s,NEAR
FFAC6F6C-1B2E-47C2-8110-5E619B239FB1,moo2,00:00:24,2014-11-11 23:20:24.730000,2014-11-11 23:20:48.750000,nkfe-cnb7s,NEAR

这也显示出不止一个值(value)。

我最近在这里看到了一个 SO 线程，讨论在这里添加到文件:How do you append to a file?但由于我仅在内存中创建此项目(使用 stringIO)，如何才能获得相同的效果？

谢谢!

编辑更多信息:

visit_list 受到访问模型的影响:

class Visit(models.Model):
    idfa = models.ForeignKey(Report) 
    name = models.CharField(max_length=255)
    lastSeen = models.CharField(max_length=255)
    duration = models.CharField(max_length=255)
    firstSeen = models.CharField(max_length=255)
    identifier = models.CharField(max_length=255)
    closestProximity = models.CharField(max_length=255)

    def __unicode__(self):
        return self.name

    class Meta:
        verbose_name = "Visit"
        verbose_name_plural = "Visits"

在这种特殊情况下，visit_list 返回:

>>> visit_list
[<Visit: PPTest1>, <Visit: moo2>]

Answer 1

底线:我怀疑您需要将 f.getvalue() 传递给 HttpResponse 而不是 f .

解释:

HttpResponse prefers strings ，尽管它也可以被视为文件对象或接受迭代器。不过，f 是一个 StringIO.StringIO 实例，而不是字符串本身。

考虑以下设置:

import StringIO
import csv

>>> f = StringIO.StringIO()
>>> writer = csv.writer(f, dialect='excel')
>>> row = range(4)                           # first row is [0, 1, 2, 3]
>>> for i in range(5):
        writer.writerow([row])               # write more rows
        row = [x + 1 for x in row]

>>> f.seek(0)

现在将 f 与 f.getvalue() 的结果进行比较:

# an instance
>>> f
<StringIO.StringIO instance at 0x03656990>

# a string
>>> f.getvalue()
'"[0, 1, 2, 3]"\r\n"[1, 2, 3, 4]"\r\n"[2, 3, 4, 5]"\r\n"[3, 4, 5, 6]"\r\n"[4, 5, 6, 7]"\r\n'

现在请注意将实例与字符串传递给 HttpResponse 时 response 对象的区别:

# The instance
>>> response = HttpResponse(f, content_type='text/csv')  # f is an instance
>>> response['Content-Disposition'] = 'attachment; filename=AdvertiserData.csv'
>>> response._container
['']

# The string
>>> response = HttpResponse(f.getvalue(), content_type='text/csv')  # f.getvalue() returns a string
>>> response['Content-Disposition'] = 'attachment; filename=AdvertiserData.csv'
>>> response._container
['"[0, 1, 2, 3]"\r\n"[1, 2, 3, 4]"\r\n"[2, 3, 4, 5]"\r\n"[3, 4, 5, 6]"\r\n"[4, 5 , 6, 7]"\r\n']

请注意，当您将实例传递给 HttpResponse 时，响应的 _container 属性为空，但当您传递 f 时，响应的 not 属性为空.getvalue() 字符串到 HttpResponse。

我会尝试这个，然后:

>>> response = HttpResponse(f.getvalue(), content_type='text/csv')
>>> # etc.