用请求用python下载大文件

Question

Requests是一个非常好的库。我想用它来下载大文件(1GB)。问题是不可能将整个文件保存在内存中;我需要分段阅读。这是下面代码的问题:

import requests
def DownloadFile(url)
    local_filename = url.split('/')[-1]
    r = requests.get(url)
    f = open(local_filename, 'wb')
    for chunk in r.iter_content(chunk_size=512 * 1024): 
        if chunk: # filter out keep-alive new chunks
            f.write(chunk)
    f.close()
    return 

由于某些原因，它不能这样工作;在保存到文件之前，它仍然会将响应加载到内存中。

Answer 1

使用以下流代码，无论下载文件大小，Python内存使用都受到限制:

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。

Answer 2

使用Response.raw和shutil.copyfileobj()就容易多了:

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

这将文件流式传输到磁盘，而不使用过多的内存，代码很简单。

注意:根据文档，Response.raw将不解码gzip和deflate传输编码，因此您需要手动执行此操作。

Answer 3

不是OP想要的，但是…用urllib:

这样做非常容易

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)

I watched the process:

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?

Answer 4

您的块大小可能太大，您是否尝试过减少它-也许一次1024字节?(也可以使用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 

顺便说一下，你是如何推断响应已经加载到内存中的?

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

    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())

Answer 5

使用python的wget模块代替。下面是一个代码片段

import wget
wget.download(url)

Answer 6

根据上面罗马人最受欢迎的评论，这里是我的实现，包括"下载"在内。和";retries"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 ''

Answer 7

这里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用asyncio库实现的(aiohttp从URL读取，aiofiles写入文件)。

下面的代码应该在Python 3.7和更高版本上工作。
复制粘贴前编辑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))

Answer 8

requests是好的，但是socket的解决方案呢?

def stream_(host):
    import socket
    import ssl
    with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
        context = ssl.create_default_context(Purpose.CLIENT_AUTH)
        with context.wrap_socket(sock, server_hostname=host) as wrapped_socket:
            wrapped_socket.connect((socket.gethostbyname(host), 443))
            wrapped_socket.send(
                "GET / HTTP/1.1rnHost:thiscatdoesnotexist.comrnAccept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9rnrn".encode())
            resp = b""
            while resp[-4:-1] != b"rnr":
                resp += wrapped_socket.recv(1)
            else:
                resp = resp.decode()
                content_length = int("".join([tag.split(" ")[1] for tag in resp.split("rn") if "content-length" in tag.lower()]))
                image = b""
                while content_length > 0:
                    data = wrapped_socket.recv(2048)
                    if not data:
                        print("EOF")
                        break
                    image += data
                    content_length -= len(data)
                with open("image.jpeg", "wb") as file:
                    file.write(image)

Answer 9

这是下载大文件的另一种选择。这将允许您稍后停止并继续(按输入键停止)，并从您离开的地方继续，否则如果您的连接断开。

import datetime
import os
import requests
import threading as th
keep_going = True
def key_capture_thread():
    global keep_going
    input()
    keep_going = False
pkey_capture = th.Thread(target=key_capture_thread, args=(), name='key_capture_process', daemon=True).start()
def download_file(url, local_filepath):
    #assumptions:
    #  headers contain Content-Length:
    #  headers contain Accept-Ranges: bytes
    #  stream is not encoded (otherwise start bytes are not known, unless this is stored seperately)
    
    chunk_size = 1048576 #1MB
    # chunk_size = 8096 #8KB
    # chunk_size = 1024 #1KB
    decoded_bytes_downloaded_this_session = 0
    start_time = datetime.datetime.now()
    if os.path.exists(local_filepath):
        decoded_bytes_downloaded = os.path.getsize(local_filepath)
    else:
        decoded_bytes_downloaded = 0
    with requests.Session() as s:
        with s.get(url, stream=True) as r:
            #check for required headers:
            if 'Content-Length' not in r.headers:
                print('STOP: request headers do not contain Content-Length')
                return
            if ('Accept-Ranges','bytes') not in r.headers.items():
                print('STOP: request headers do not contain Accept-Ranges: bytes')
                with s.get(url) as r:
                    print(str(r.content, encoding='iso-8859-1'))
                return
        content_length = int(r.headers['Content-Length'])
        if decoded_bytes_downloaded>=content_length:
                print('STOP: file already downloaded. decoded_bytes_downloaded>=r.headers[Content-Length]; {}>={}'.format(decoded_bytes_downloaded,r.headers['Content-Length']))
                return
        if decoded_bytes_downloaded>0:
            s.headers['Range'] = 'bytes={}-{}'.format(decoded_bytes_downloaded, content_length-1) #range is inclusive
            print('Retrieving byte range (inclusive) {}-{}'.format(decoded_bytes_downloaded, content_length-1))
        with s.get(url, stream=True) as r:
            r.raise_for_status()
            with open(local_filepath, mode='ab') as fwrite:
                for chunk in r.iter_content(chunk_size=chunk_size):
                    decoded_bytes_downloaded+=len(chunk)
                    decoded_bytes_downloaded_this_session+=len(chunk)
                    time_taken:datetime.timedelta = (datetime.datetime.now() - start_time)
                    seconds_per_byte = time_taken.total_seconds()/decoded_bytes_downloaded_this_session
                    remaining_bytes = content_length-decoded_bytes_downloaded
                    remaining_seconds = seconds_per_byte * remaining_bytes
                    remaining_time = datetime.timedelta(seconds=remaining_seconds)
                    #print updated statistics here
                    fwrite.write(chunk)
                    if not keep_going:
                        break
output_folder = '/mnt/HDD1TB/DownloadsBIG'
# url = 'https://file-examples.com/storage/fea508993d645be1b98bfcf/2017/10/file_example_JPG_100kB.jpg'
# url = 'https://file-examples.com/storage/fe563fce08645a90397f28d/2017/10/file_example_JPG_2500kB.jpg'
url = 'https://ftp.ncbi.nlm.nih.gov/blast/db/nr.00.tar.gz'
local_filepath = os.path.join(output_folder, os.path.split(url)[-1])
download_file(url, local_filepath)