为什么我无法使用Python3.x中的urllib通过代理下载？

Question

我试图编写一个脚本，通过代理下载一个文件，并以Minecraft的可执行文件为例。代理似乎不起作用

我尝试过更改代理IP地址，但在使用urllib.request.getproxies()列出代理时，什么也没有出现

以下是我为解决此问题而查看的一些链接，包括StackOverflow和官方文档上的帖子：

urllib.request.urlretrieve with proxy?

Python urllib urlretrieve behind proxy

https://docs.python.org/3.5/library/urllib.request.html#urllib.request.ProxyHandler

https://www.programcreek.com/python/example/75591/urllib.request.ProxyHandler

https://docs.python.org/3/howto/urllib2.html

理想情况下，我希望继续使用这个库，因为有些计算机没有安装像requests这样的库，我希望它在任何地方都可以开箱即用，而不需要下载额外的东西

编辑：我的代码非常仓促，写得很糟糕，对此我深表歉意。整个项目比任何其他项目都更能证明概念

import urllib.request
import sys
import os
import subprocess

# URL with port for proxy server (find one at hidester.com)
proxyurl = "IP ADDRESS HERE - I have tried several"
useproxy = True

# Set constants for easy editing later
downloadurl = "https://launcher.mojang.com/download/"
downloadfilename = "Minecraft.exe"
launcherfilename = "launch_minecraft.bat"

downloadpath = os.path.join("bin", downloadfilename)

def main():
    print("Setting up...\n")

    # Inital setup - create necessary paths
    if not os.path.exists("bin"):
        os.makedirs("bin")

    if not os.path.exists("data"):
        os.makedirs("data")

    if not os.path.exists(downloadpath):
        download()
    else:
        print("Minecraft has already been downloaded! Download again?")
        choice = input("[Y/n]: ")

        if choice == "y" or choice == "Y":
            try:
                os.remove(downloadpath)
            except:
                exit("ERROR: Could not remove file.")

            download()

    if not os.path.exists(launcherfilename):
        createbatch()


    print("==== Setup complete! ====\n")
    launchgame()

def download():
    if useproxy == True:
        # Setup proxy handler
        proxy = urllib.request.ProxyHandler({'http': proxyurl})
        opener = urllib.request.build_opener(proxy)
        urllib.request.install_opener(opener)

        if len(urllib.request.getproxies()) < 1:
            exit("ERROR: No proxy!")

        print('Downloading file from "{0}" using proxy server "{1}"\n'.format(downloadurl, proxyurl))

    else:
        # Not using proxy
        print('Downloading file from "{0}" without proxy\n'.format(downloadurl))

    # Download latest EXE
    try:
        urllib.request.urlretrieve(downloadurl + downloadfilename, downloadpath, reporthook)
        print("Download finished!\n")
    except:
        exit("ERROR: Could not download file.")


def createbatch():
    # Create a file to launch the launcher with the correct working directory
    # NOTE: I download the file from GitHub here rather than writing directly to a file to avoid the weirdness with Unicode characters in Python.
    print("Downloading launcher file...")

    if os.name == "nt":
        try:
            urllib.request.urlretrieve("https://gist.githubusercontent.com/iCrazyBlaze/a8a3fdf89377a901a250f4a36c459415/raw/d66d0e9b7fa06836c33d8254504496a9b65d591a/launch_minecraft.bat", launcherfilename)
            print("Download finished!\n")
        except:
            print("ERROR: Could not download file.")

def launchgame():
    if os.name == "nt":
        subprocess.call(launcherfilename)

# Display progress on screen
def reporthook(blocknum, blocksize, totalsize):
    readsofar = blocknum * blocksize
    if totalsize > 0:
        percent = readsofar * 1e2 / totalsize
        s = "\r%5.1f%% %*d / %d" % (
            percent, len(str(totalsize)), readsofar, totalsize)
        sys.stderr.write(s)
        if readsofar >= totalsize: # near the end
            sys.stderr.write("\n")
    else: # total size is unknown
        sys.stderr.write("Read %d\n" % (readsofar,))


if __name__ == "__main__":
    main()