使用Python请求"桥接"文件而不加载到内存中？

Question

我想使用Python Requests库从URL获取文件,并在post请求中将其用作mulitpart编码文件.问题是该文件可能非常大(50MB-2GB),我不想将其加载到内存中.(上下文这里.)

下面的文档中的示例(multipart,stream down和stream up)我做了这样的事情:

    with requests.get(big_file_url, stream=True) as f:
        requests.post(upload_url, files={'file': ('filename', f.content)})

但我不确定我做得对.它实际上是抛出这个错误 - 从追溯中编辑:

    with requests.get(big_file_url, stream=True) as f:
    AttributeError: __exit__

有什么建议？

Answer 1

正如其他答案已经指出的那样：requests不支持 POSTing 多部分编码文件而不将其加载到内存中。

要上传大文件而不使用 multipart/form-data 将其加载到内存中，您可以使用poster：

#!/usr/bin/env python
import sys
from urllib2 import Request, urlopen

from poster.encode import multipart_encode # $ pip install poster
from poster.streaminghttp import register_openers

register_openers() # install openers globally

def report_progress(param, current, total):
    sys.stderr.write("\r%03d%% of %d" % (int(1e2*current/total + .5), total))

url = 'http://example.com/path/'
params = {'file': open(sys.argv[1], "rb"), 'name': 'upload test'}
response = urlopen(Request(url, *multipart_encode(params, cb=report_progress)))
print response.read()

它可以进行调整以允许 GET 响应对象而不是本地文件：

import posixpath
import sys
from urllib import unquote
from urllib2 import Request, urlopen
from urlparse import urlsplit

from poster.encode import MultipartParam, multipart_encode # pip install poster
from poster.streaminghttp import register_openers

register_openers() # install openers globally

class MultipartParamNoReset(MultipartParam):
    def reset(self):
        pass # do nothing (to allow self.fileobj without seek() method)

get_url = 'http://example.com/bigfile'
post_url = 'http://example.com/path/'

get_response = urlopen(get_url)
param = MultipartParamNoReset(
    name='file',
    filename=posixpath.basename(unquote(urlsplit(get_url).path)), #XXX \ bslash
    filetype=get_response.headers['Content-Type'],
    filesize=int(get_response.headers['Content-Length']),
    fileobj=get_response)

params = [('name', 'upload test'), param]
datagen, headers = multipart_encode(params, cb=report_progress)
post_response = urlopen(Request(post_url, datagen, headers))
print post_response.read()

Content-Length此解决方案需要GET 响应中的有效标头（已知文件大小）。如果文件大小未知，则可以使用分块传输编码来上传多部分/表单数据内容。可以使用库urllib3.filepost附带的解决方案来实现类似的解决方案requests，例如，基于@AdrienF 的答案，而不使用poster.

Answer 2

实际上，Kenneth Reitz 的 GitHub存储库上有一个与此相关的问题。我遇到了同样的问题（尽管我只是上传本地文件），我添加了一个包装类，它是与请求的不同部分相对应的流列表，并带有一个迭代列表的 read() 属性，读取每个部分，并获取标题的必要值（边界和内容长度）：

# coding=utf-8

from __future__ import unicode_literals
from mimetools import choose_boundary
from requests.packages.urllib3.filepost import iter_fields, get_content_type
from io import BytesIO
import codecs

writer = codecs.lookup('utf-8')[3]

class MultipartUploadWrapper(object):

    def __init__(self, files):
        """
        Initializer

        :param files:
            A dictionary of files to upload, of the form {'file': ('filename', <file object>)}
        :type network_down_callback:
            Dict
        """
        super(MultipartUploadWrapper, self).__init__()
        self._cursor = 0
        self._body_parts = None
        self.content_type_header = None
        self.content_length_header = None
        self.create_request_parts(files)

    def create_request_parts(self, files):
        request_list = []
        boundary = choose_boundary()
        content_length = 0

        boundary_string = b'--%s\r\n' % (boundary)
        for fieldname, value in iter_fields(files):
            content_length += len(boundary_string)

            if isinstance(value, tuple):
                filename, data = value
                content_disposition_string = (('Content-Disposition: form-data; name="%s"; ''filename="%s"\r\n' % (fieldname, filename))
                                            + ('Content-Type: %s\r\n\r\n' % (get_content_type(filename))))

            else:
                data = value
                content_disposition_string =  (('Content-Disposition: form-data; name="%s"\r\n' % (fieldname))
                                            + 'Content-Type: text/plain\r\n\r\n')
            request_list.append(BytesIO(str(boundary_string + content_disposition_string)))
            content_length += len(content_disposition_string)
            if hasattr(data, 'read'):
                data_stream = data
            else:
                data_stream = BytesIO(str(data))

            data_stream.seek(0,2)
            data_size = data_stream.tell()
            data_stream.seek(0)

            request_list.append(data_stream)
            content_length += data_size

            end_string = b'\r\n'
            request_list.append(BytesIO(end_string))
            content_length += len(end_string)

        request_list.append(BytesIO(b'--%s--\r\n' % (boundary)))
        content_length += len(boundary_string)

        # There's a bug in httplib.py that generates a UnicodeDecodeError on binary uploads if
        # there are *any* unicode strings passed into headers as part of the requests call.
        # For this reason all strings are explicitly converted to non-unicode at this point.
        self.content_type_header = {b'Content-Type': b'multipart/form-data; boundary=%s' % boundary}
        self.content_length_header = {b'Content-Length': str(content_length)}
        self._body_parts = request_list

    def read(self, chunk_size=0):
        remaining_to_read = chunk_size
        output_array = []
        while remaining_to_read > 0:
            body_part = self._body_parts[self._cursor]
            current_piece = body_part.read(remaining_to_read)
            length_read = len(current_piece)
            output_array.append(current_piece)
            if length_read < remaining_to_read:
                # we finished this piece but haven't read enough, moving on to the next one
                remaining_to_read -= length_read
                if self._cursor == len(self._body_parts) - 1:
                    break
                else:
                    self._cursor += 1
            else:
                break
        return b''.join(output_array)

因此，您可以将此对象作为“data”属性传递给 Request.request 对象，而不是传递“files”关键字arg

编辑

我已经清理了代码