如果使用响应，就简单多了。Raw和shutil.copyfileobj():

import requests
import shutil

def download_file(url):
    local_filename = url.split('/')[-1]
    with requests.get(url, stream=True) as r:
        with open(local_filename, 'wb') as f:
            shutil.copyfileobj(r.raw, f)

    return local_filename

这样可以在不使用过多内存的情况下将文件流到磁盘，而且代码很简单。

注:根据文档，响应。Raw不会解码gzip和压缩传输编码，因此您需要手动执行此操作。

使用以下流代码，无论下载的文件大小如何，Python内存使用都会受到限制:

def download_file(url):
    local_filename = url.split('/')[-1]
    # NOTE the stream=True parameter below
    with requests.get(url, stream=True) as r:
        r.raise_for_status()
        with open(local_filename, 'wb') as f:
            for chunk in r.iter_content(chunk_size=8192): 
                # If you have chunk encoded response uncomment if
                # and set chunk_size parameter to None.
                #if chunk: 
                f.write(chunk)
    return local_filename

注意，使用iter_content返回的字节数并不完全是chunk_size;它通常是一个大得多的随机数，并且在每次迭代中都是不同的。

参见body-content-workflow和Response。Iter_content供进一步参考。

您的块大小可能太大了，您是否尝试过删除它-可能一次1024字节?(同时，你可以使用with来整理语法)

def DownloadFile(url):
    local_filename = url.split('/')[-1]
    r = requests.get(url)
    with open(local_filename, 'wb') as f:
        for chunk in r.iter_content(chunk_size=1024): 
            if chunk: # filter out keep-alive new chunks
                f.write(chunk)
    return 

顺便提一下，您如何推断响应已加载到内存中?

听起来好像python没有将数据刷新到文件中，从其他SO问题中，您可以尝试f.flush()和os.fsync()来强制写入文件并释放内存;

    with open(local_filename, 'wb') as f:
        for chunk in r.iter_content(chunk_size=1024): 
            if chunk: # filter out keep-alive new chunks
                f.write(chunk)
                f.flush()
                os.fsync(f.fileno())

这不是OP想问的，但是…使用urllib非常容易做到这一点:

from urllib.request import urlretrieve

url = 'http://mirror.pnl.gov/releases/16.04.2/ubuntu-16.04.2-desktop-amd64.iso'
dst = 'ubuntu-16.04.2-desktop-amd64.iso'
urlretrieve(url, dst)

或者这样，如果你想把它保存到一个临时文件:

from urllib.request import urlopen
from shutil import copyfileobj
from tempfile import NamedTemporaryFile

url = 'http://mirror.pnl.gov/releases/16.04.2/ubuntu-16.04.2-desktop-amd64.iso'
with urlopen(url) as fsrc, NamedTemporaryFile(delete=False) as fdst:
    copyfileobj(fsrc, fdst)

我观察了整个过程:

watch 'ps -p 18647 -o pid,ppid,pmem,rsz,vsz,comm,args; ls -al *.iso'

我看到文件在增长，但内存使用量保持在17 MB。我错过了什么吗?

下面是异步分块下载用例的另一种方法，无需将所有文件内容读入内存。 这意味着从URL读取和写入文件都是使用asyncio库实现的(aiohttp从URL读取，aiofiles写入文件)。

以下代码应该适用于Python 3.7及更高版本。 复制粘贴前只需编辑SRC_URL和DEST_FILE变量。

import aiofiles
import aiohttp
import asyncio

async def async_http_download(src_url, dest_file, chunk_size=65536):
    async with aiofiles.open(dest_file, 'wb') as fd:
        async with aiohttp.ClientSession() as session:
            async with session.get(src_url) as resp:
                async for chunk in resp.content.iter_chunked(chunk_size):
                    await fd.write(chunk)

SRC_URL = "/path/to/url"
DEST_FILE = "/path/to/file/on/local/machine"

asyncio.run(async_http_download(SRC_URL, DEST_FILE))

根据上面Roman被点赞最多的评论，下面是我的实现， 包括“下载为”和“重试”机制:

def download(url: str, file_path='', attempts=2):
    """Downloads a URL content into a file (with large file support by streaming)

    :param url: URL to download
    :param file_path: Local file name to contain the data downloaded
    :param attempts: Number of attempts
    :return: New file path. Empty string if the download failed
    """
    if not file_path:
        file_path = os.path.realpath(os.path.basename(url))
    logger.info(f'Downloading {url} content to {file_path}')
    url_sections = urlparse(url)
    if not url_sections.scheme:
        logger.debug('The given url is missing a scheme. Adding http scheme')
        url = f'http://{url}'
        logger.debug(f'New url: {url}')
    for attempt in range(1, attempts+1):
        try:
            if attempt > 1:
                time.sleep(10)  # 10 seconds wait time between downloads
            with requests.get(url, stream=True) as response:
                response.raise_for_status()
                with open(file_path, 'wb') as out_file:
                    for chunk in response.iter_content(chunk_size=1024*1024):  # 1MB chunks
                        out_file.write(chunk)
                logger.info('Download finished successfully')
                return file_path
        except Exception as ex:
            logger.error(f'Attempt #{attempt} failed with error: {ex}')
    return ''