有效地与请求异步下载文件

Question

我想用python尽可能快地下载文件。这是我的代码

import pandas as pd
import requests
from requests_futures.sessions import FuturesSession
import os
import pathlib
from timeit import default_timer as timer


class AsyncDownloader:
    """Download files asynchronously"""

    __urls = set()
    __dest_path = None
    __user_agent = 'Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0'
    __read_timeout = 60
    __connection_timeout = 30
    __download_count = 0  # unlimited
    # http://www.browserscope.org/?category=network
    __worker_count = 17  # No of threads to spawn
    __chunk_size = 1024
    __download_time = -1
    __errors = []

    # TODO Fetch only content of a specific type from a csv
    # TODO Improve code structure so that it can be used as a commandline tool

    def set_source_csv(self, source_path, column_name):
        self.source_path = source_path
        self.column_name = column_name

        try:
            my_csv = pd.read_csv(source_path, usecols=[self.column_name], chunksize=10)
        except ValueError:
            print("The column name doesn't exist")
            return
        else:
            # No exception whatsoever
            for chunk in my_csv:
                AsyncDownloader.__urls.update(set(getattr(chunk, self.column_name)))

    def set_destination_path(self, dest_path):
        if dest_path.endswith('/'):
            dest_path = dest_path[:-1]
        self.dest_path = dest_path
        # TODO Add exception in case we can't create the directory
        pathlib.Path(self.dest_path).mkdir(parents=True, exist_ok=True)
        if os.access(self.dest_path, os.W_OK):
            AsyncDownloader.__dest_path = pathlib.Path(self.dest_path).resolve()

    def set_user_agent(self, useragent):
        self.useragent = useragent
        AsyncDownloader.__user_agent = self.useragent

    def set_connection_timeout(self, ctimeout_secs):
        self.timeout_secs = ctimeout_secs
        if self.timeout_secs >= 0:
            AsyncDownloader.__connection_timeout = self.timeout_secs

    def set_read_timeout(self, rtimeout_secs):
        self.timeout_secs = rtimeout_secs
        if self.timeout_secs >= 0:
            AsyncDownloader.__read_timeout = self.timeout_secs

    def set_download_count(self, file_count):
        self.file_count = file_count
        if self.file_count > 0:
            AsyncDownloader.__download_count = self.file_count

    def set_worker_count(self, worker_count):
        self.worker_count = worker_count
        if self.worker_count > 0:
            AsyncDownloader.__worker_count = self.worker_count

    def set_chunk_size(self, chunk_size):
        self.chunk_size = chunk_size
        if self.chunk_size > 0:
            AsyncDownloader.__chunk_size = self.chunk_size

    def print_urls(self):
        print(AsyncDownloader.__urls)

    def get_download_time(self):
        return AsyncDownloader.__download_time

    def get_errors(self):
        return AsyncDownloader.__errors

    def download(self):
        start = timer()
        try:
            session = FuturesSession(max_workers=AsyncDownloader.__worker_count)
            session.headers.update({'user-agent': AsyncDownloader.__user_agent})
            session.request(AsyncDownloader.__connection_timeout,
                            AsyncDownloader.__connection_timeout, stream=True)

            results = []
            # Give an accurate file count even if we don't have to download it as it a;ready exist
            file_count = 0

            for url in AsyncDownloader.__urls:
                filename = os.path.basename(url)
                # check if we need only a limited number of files
                if AsyncDownloader.__download_count != 0:
                    # No need to download file if it already exist
                    if pathlib.Path(AsyncDownloader.__dest_path / filename).is_file():
                        file_count += 1
                        continue
                    else:
                        if file_count < AsyncDownloader.__download_count:
                            file_count += 1
                            results.append(session.get(url))
                else:
                    if not pathlib.Path(AsyncDownloader.__dest_path / filename).is_file():
                        results.append(session.get(url))

            for result in results:
                # wait for the response to complete, if it hasn't already
                response = result.result()
                filename = os.path.basename(response.url)
                if response.status_code == 200:
                    with open(pathlib.Path(AsyncDownloader.__dest_path / filename).resolve(), 'wb') as fd:
                        for chunk in response.iter_content(chunk_size=AsyncDownloader.__chunk_size):
                            if chunk:  # filter out keep-alive new chunks
                                fd.write(chunk)

            end = timer()
            AsyncDownloader.__download_time = end - start

        except requests.exceptions.HTTPError as errh:
            AsyncDownloader.__errors.append("Http Error:" + errh)
            # print("Http Error:", errh)
        except requests.exceptions.ConnectionError as errc:
            AsyncDownloader.__errors.append("Error Connecting:" + errc)
            # print("Error Connecting:", errc)
        except requests.exceptions.Timeout as errt:
            AsyncDownloader.__errors.append("Timeout Error:" + errt)
            # print("Timeout Error:", errt)
        except requests.exceptions.RequestException as err:
            AsyncDownloader.__errors.append("OOps: Something Else" + err)
        else:
            return

下面的代码做了一个非常糟糕的假设。事实上，我假设第一个网址将首先完成，当然这是不正确的。

# wait for the response to complete, if it hasn't already
response = result.result()

如何确保只处理已完成的请求，而不是以有效的方式采取上述假设？

我将不胜感激任何有关如何提高性能的建议。

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