我正在创建一个程序，该程序将通过读取同一游戏/应用程序的.jad文件中指定的URL从Web服务器下载.jar（java）文件。我正在使用Python 3.2.1

我设法从JAD文件中提取JAR文件的URL（每个JAD文件都包含指向JAR文件的URL），但是正如您所想象的，提取的值是type（）字符串。

相关功能如下：

def downloadFile(URL=None):
    import httplib2
    h = httplib2.Http(".cache")
    resp, content = h.request(URL, "GET")
    return content

downloadFile(URL_from_file)

但是，我总是得到一个错误，指出上面函数中的类型必须是字节，而不是字符串。我尝试使用URL.encode（'utf-8'）和字节（URL，encoding ='utf-8'），但是我总是会遇到相同或相似的错误。

因此，基本上我的问题是，当URL以字符串类型存储时，如何从服务器下载文件？

如果要将网页的内容转换为变量，则只需read响应urllib.request.urlopen：

import urllib.request
...
url = 'http://example.com/'
response = urllib.request.urlopen(url)
data = response.read()      # a `bytes` object
text = data.decode('utf-8') # a `str`; this step can't be used if data is binary

下载和保存文件的最简单方法是使用以下urllib.request.urlretrieve功能：

import urllib.request
...
# Download the file from `url` and save it locally under `file_name`:
urllib.request.urlretrieve(url, file_name)

import urllib.request
...
# Download the file from `url`, save it in a temporary directory and get the
# path to it (e.g. '/tmp/tmpb48zma.txt') in the `file_name` variable:
file_name, headers = urllib.request.urlretrieve(url)

但是请记住，这urlretrieve被认为是遗留的，并且可能会被弃用（尽管不确定为什么）。

因此，最正确的方法是使用urllib.request.urlopen函数返回代表HTTP响应的类似文件的对象，然后使用将其复制到真实文件中shutil.copyfileobj。

import urllib.request
import shutil
...
# Download the file from `url` and save it locally under `file_name`:
with urllib.request.urlopen(url) as response, open(file_name, 'wb') as out_file:
    shutil.copyfileobj(response, out_file)

如果这看起来太复杂，则可能要简化一些并将整个下载存储在一个bytes对象中，然后将其写入文件。但这仅适用于小文件。

import urllib.request
...
# Download the file from `url` and save it locally under `file_name`:
with urllib.request.urlopen(url) as response, open(file_name, 'wb') as out_file:
    data = response.read() # a `bytes` object
    out_file.write(data)

可以动态提取.gz（可能还有其他格式）压缩数据，但是这种操作可能需要HTTP服务器支持对文件的随机访问。

import urllib.request
import gzip
...
# Read the first 64 bytes of the file inside the .gz archive located at `url`
url = 'http://example.com/something.gz'
with urllib.request.urlopen(url) as response:
    with gzip.GzipFile(fileobj=response) as uncompressed:
        file_header = uncompressed.read(64) # a `bytes` object
        # Or do anything shown above using `uncompressed` instead of `response`.

requests每当我想要与HTTP请求相关的内容时，我都会使用package，因为它的API很容易开头：

首先，安装 requests

$ pip install requests

然后是代码：

from requests import get  # to make GET request


def download(url, file_name):
    # open in binary mode
    with open(file_name, "wb") as file:
        # get request
        response = get(url)
        # write to file
        file.write(response.content)

我希望我理解正确的问题，那就是：当URL以字符串类型存储时，如何从服务器下载文件？

我下载文件并使用以下代码将其保存在本地：

import requests

url = 'https://www.python.org/static/img/python-logo.png'
fileName = 'D:\Python\dwnldPythonLogo.png'
req = requests.get(url)
file = open(fileName, 'wb')
for chunk in req.iter_content(100000):
    file.write(chunk)
file.close()

在这里，我们可以在Python3中使用urllib的Legacy接口：

以下函数和类是从Python 2模块urllib（与urllib2相对）移植的。他们可能在将来的某个时候被弃用。

示例（两行代码）：

import urllib.request

url = 'https://www.python.org/static/img/python-logo.png'
urllib.request.urlretrieve(url, "logo.png")

您可以使用wget，它是流行的下载shell工具。https://pypi.python.org/pypi/wget 这将是最简单的方法，因为它不需要打开目标文件。这是一个例子。

import wget
url = 'https://i1.wp.com/python3.codes/wp-content/uploads/2015/06/Python3-powered.png?fit=650%2C350'  
wget.download(url, '/Users/scott/Downloads/cat4.jpg') 

是的，绝对请求是用于与HTTP请求相关的东西的很好的程序包。但是我们需要注意传入数据的编码类型，下面是一个说明差异的示例

from requests import get

# case when the response is byte array
url = 'some_image_url'

response = get(url)
with open('output', 'wb') as file:
    file.write(response.content)


# case when the response is text
# Here unlikely if the reponse content is of type **iso-8859-1** we will have to override the response encoding
url = 'some_page_url'

response = get(url)
# override encoding by real educated guess as provided by chardet
r.encoding = r.apparent_encoding

with open('output', 'w', encoding='utf-8') as file:
    file.write(response.content)

动机

有时，我们想要获取图片，但无需将其下载到真实文件中，

即下载数据并将其保存在内存中。

例如，如果我使用机器学习方法，则训练一个可以识别带有数字（条形码）图像的模型。

当我搜寻一些具有这些图像的网站时，我可以使用模型来识别它，

而且我不想将这些图片保存在磁盘驱动器上，

那么您可以尝试以下方法来帮助您将下载数据保留在内存中。

点数

import requests
from io import BytesIO
response = requests.get(url)
with BytesIO as io_obj:
    for chunk in response.iter_content(chunk_size=4096):
        io_obj.write(chunk)

基本上，就像@Ranvijay Kumar

一个例子

import requests
from typing import NewType, TypeVar
from io import StringIO, BytesIO
import matplotlib.pyplot as plt
import imageio

URL = NewType('URL', str)
T_IO = TypeVar('T_IO', StringIO, BytesIO)


def download_and_keep_on_memory(url: URL, headers=None, timeout=None, **option) -> T_IO:
    chunk_size = option.get('chunk_size', 4096)  # default 4KB
    max_size = 1024 ** 2 * option.get('max_size', -1)  # MB, default will ignore.
    response = requests.get(url, headers=headers, timeout=timeout)
    if response.status_code != 200:
        raise requests.ConnectionError(f'{response.status_code}')

    instance_io = StringIO if isinstance(next(response.iter_content(chunk_size=1)), str) else BytesIO
    io_obj = instance_io()
    cur_size = 0
    for chunk in response.iter_content(chunk_size=chunk_size):
        cur_size += chunk_size
        if 0 < max_size < cur_size:
            break
        io_obj.write(chunk)
    io_obj.seek(0)
    """ save it to real file.
    with open('temp.png', mode='wb') as out_f:
        out_f.write(io_obj.read())
    """
    return io_obj


def main():
    headers = {
        'Accept': 'text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3',
        'Accept-Encoding': 'gzip, deflate',
        'Accept-Language': 'zh-TW,zh;q=0.9,en-US;q=0.8,en;q=0.7',
        'Cache-Control': 'max-age=0',
        'Connection': 'keep-alive',
        'Host': 'statics.591.com.tw',
        'Upgrade-Insecure-Requests': '1',
        'User-Agent': 'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.87 Safari/537.36'
    }
    io_img = download_and_keep_on_memory(URL('http://statics.591.com.tw/tools/showPhone.php?info_data=rLsGZe4U%2FbphHOimi2PT%2FhxTPqI&type=rLEFMu4XrrpgEw'),
                                         headers,  # You may need this. Otherwise, some websites will send the 404 error to you.
                                         max_size=4)  # max loading < 4MB
    with io_img:
        plt.rc('axes.spines', top=False, bottom=False, left=False, right=False)
        plt.rc(('xtick', 'ytick'), color=(1, 1, 1, 0))  # same of plt.axis('off')
        plt.imshow(imageio.imread(io_img, as_gray=False, pilmode="RGB"))
        plt.show()


if __name__ == '__main__':
    main()

from urllib import request

def get(url):
    with request.urlopen(url) as r:
        return r.read()


def download(url, file=None):
    if not file:
        file = url.split('/')[-1]
    with open(file, 'wb') as f:
        f.write(get(url))