如何检查要完成下载 Python3 的文件？

Question

我正在尝试弄清楚如何检查下载是否已完成。基本上我希望它等到文件完成下载然后打印：下载完成。

这是我当前的代码以及我想用它做什么：

from  urllib import request

print("Are you sure you want to download the newest file? y/n")
answer = input()

while True:
    if answer == 'y':
        print("Downloading file...")
        downloading = True
        request.urlretrieve("FILE_URL", "FILE_NAME")
    elif answer == 'n':
         exit()
    else:
         print("That is not a valid answer, please answer with y/n.")
         answer = input()

#I need some sort of function here that checks if the file is still being 
#downloaded

when downloading == False:
    print("Download Completed.")

Answer 1

如果您使用urllib.request.urlretrieve reporthook 选项，您可以监控下载进度，尤其适用于大文件，如下所示：

import urllib.request

def Download_Progress(block_num, block_size, total_size):
    downloaded = block_num * block_size
    progress = int((downloaded/total_size)*100)
    print ("Download Progress",str(progress),"%")

url = "https://somesite/some.pdf"
urllib.request.urlretrieve(url, 'mycopy.pdf', reporthook=Download_Progress)
print ("Finished")

您也可以使用requests 包实现类似的功能。

import requests
url = "https://somesite/some.pdf"

#Get the headers of the remote file
h = requests.head(url, allow_redirects=True)

#Get the size of the file
total_size = int(h.headers.get('content-length'))

#Request the file download with stream set to True
r = requests.get(url, stream=True)

#Open a local file for writing
localfile = open("mycopy.pdf", "wb")
chunks = 0

#Process the file as it arrives
for chunk in r.iter_content(chunk_size=512):
    if chunk:
        chunks += 1
        downloaded = chunks * 512
        # An approximation as the chunks don't have to be 512 bytes
        progress = int((downloaded/total_size)*100)
        print ("Download Progress",str(progress),"%")
        localfile.write(chunk)
print("Finished")

Answer 2

当urlretrieve返回时，文件已经下载完毕。

参见docs中的用法示例：

>>> import urllib.request
>>> local_filename, headers = urllib.request.urlretrieve('http://python.org/')
>>> html = open(local_filename)

可以看出，文件在调用urlretrieve 后立即打开，因为它已经创建并且内容已经写入那里。