请检查代码错误并修正最后优化代码。代码：Pythonimport sysimport osimport mathimport timeimport requestsimport urllibrequestimport threadingfrom urllibparse import urlparsefrom tqdm import tqdmclass DownloadThreadthreading

import sys import os import math import time import requests import urllib.request import threading from urllib.parse import urlparse from tqdm import tqdm

class DownloadThread(threading.Thread): def init(self, url, start, end, fileobj, bar): threading.Thread.init(self) self.url = url self.start = start self.end = end self.fileobj = fileobj self.bar = bar

def run(self):
    headers = {'Range': 'bytes=%d-%d' % (self.start, self.end)}
    response = requests.get(self.url, headers=headers, stream=True)
    for chunk in response.iter_content(chunk_size=1024):
        if not chunk:
            break
        self.fileobj.write(chunk)
        self.bar.update(len(chunk))

class FTPDownloadThread(threading.Thread): def init(self, ftp_url, start, end, fileobj, bar): threading.Thread.init(self) self.ftp_url = ftp_url self.start = start self.end = end self.fileobj = fileobj self.bar = bar

def run(self):
    req = urllib.request.urlopen(self.ftp_url)
    req.sendcmd("TYPE I")
    fileSize = int(req.headers['Content-Length'])

    ftp = urllib.request.urlopen(self.ftp_url)
    for i in ["RETR {}".format(os.path.basename(self.ftp_url))]:
        ftp.sendcmd(i)
    ftp.settimeout(60)

    ftp_read = True
    while ftp_read:
        data = ftp.read(1024)
        if not data:
            break

        self.fileobj.write(data)
        self.bar.update(len(data))
    ftp.close()

def download_file(url: str, filename: str, num_threads: int = 4) -> None: os.makedirs("Download", exist_ok=True) filename = os.path.join("Download", filename) response = requests.get(url, stream=True) if 'Content-Length' in response.headers: file_size = int(response.headers['Content-Length']) else: print("The file size is unknown, use single thread download.") download_single_thread(url=url, filename=filename) return

# 判断文件大小是否为0
if file_size == 0:
    raise ValueError("Failed to get file size, please check the download URL")

with open(filename, 'wb') as file:
    with tqdm(total=file_size, unit='B', unit_scale=True,
              desc=os.path.basename(filename), ncols=80, position=0) as bar:

        download_time = 0
        chunk_size = 1024
        avg_speed = 0
        last_speed = 0
        while True:
            start = time.time()
            chunk = response.raw.read(chunk_size*num_threads)
            end = time.time()

            if not chunk:
                break

            used_time = end - start
            download_time += used_time

            speed = chunk_size*num_threads/used_time
            avg_speed = (avg_speed + speed) / 2

            if avg_speed > 0:
                last_speed = avg_speed
                num_threads = int(file_size / avg_speed / chunk_size) + 1
            num_threads = min(max(num_threads, 1), 32)

            thread_pool = []
            start = 0
            end = -1
            for i in range(num_threads):
                start = end + 1
                end = start + chunk_size - 1

                if i == num_threads - 1:
                    end = file_size - 1

                thread = DownloadThread(url=url, start=start, end=end, fileobj=file, bar=bar)
                thread.setDaemon(True)
                thread_pool.append(thread)

            for thread in thread_pool:
                thread.start()

            for thread in thread_pool:
                thread.join()

            bar.update(chunk_size*num_threads)

        bar.close()

return filename

def download_ftp(input_str: str, filename: str, num_threads: int = 4) -> None: os.makedirs("Download", exist_ok=True) filename = os.path.join("Download", filename) o = urlparse(input_str)

if o.scheme != 'ftp':
    raise ValueError(f"{input_str} is not an FTP URL.")

ftp_url = input_str
ftp_file_size = -1
req = urllib.request.urlopen(ftp_url)
if "Content-Length" in req.headers:
    ftp_file_size = int(req.headers["Content-Length"])

with open(filename, 'wb') as file:
    with tqdm(total=ftp_file_size, unit='B', unit_scale=True,
              desc=os.path.basename(filename), ncols=80, position=0) as bar:

        thread_pool = []
        chunk_size = 1024
        if ftp_file_size < 0:
            thread = FTPDownloadThread(ftp_url, 0, 0xFFFFFFFF, file, bar)
            thread.setDaemon(True)
            thread_pool.append(thread)

        else:
            download_time = 0
            avg_speed = 0
            last_speed = 0
            while True:
                start = time.time()
                chunk = urllib.request.urlopen(ftp_url).read(chunk_size*num_threads)
                end = time.time()

                if not chunk:
                    break

                used_time = end - start
                download_time += used_time

                speed = chunk_size*num_threads/used_time
                avg_speed = (avg_speed + speed) / 2

                if avg_speed > 0:
                    last_speed = avg_speed
                    num_threads = int(ftp_file_size / avg_speed / chunk_size) + 1
                num_threads = min(max(num_threads, 1), 32)

                thread_pool = []
                start = 0
                end = -1
                for i in range(num_threads):
                    start = end + 1
                    end = start + chunk_size - 1

                    if i == num_threads - 1:
                        end = ftp_file_size - 1

                    thread = FTPDownloadThread(ftp_url=ftp_url, start=start, end=end, fileobj=file, bar=bar)
                    thread.setDaemon(True)
                    thread_pool.append(thread)

                for thread in thread_pool:
                    thread.start()

                for thread in thread_pool:
                    thread.join()

                bar.update(chunk_size*num_threads)

        bar.close()

return filename

def download_single_thread(url: str, filename: str) -> None: response = requests.get(url, stream=True) with open(filename, 'wb') as f: for chunk in response.iter_content(chunk_size=1024): if chunk: f.write(chunk