在python3中从web下载文件

我正在创建一个程序，将下载一个。jar (java)文件从一个web服务器，通过读取URL指定在同一游戏/应用程序的。jad文件。我使用的是Python 3.2.1

我已经设法从JAD文件中提取JAR文件的URL(每个JAD文件都包含到JAR文件的URL)，但是正如您想象的那样，提取的值是type()字符串。

这是相关的函数:

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


downloadFile(URL_from_file)

然而，我总是得到一个错误，说在上面的函数的类型必须是字节，而不是字符串。我尝试使用URL.encode('utf-8')，也字节(URL,encoding='utf-8')，但我总是得到相同或类似的错误。

所以基本上我的问题是如何从服务器下载文件时，URL存储在字符串类型?

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最佳答案

如果你想获取一个网页的内容转换成一个变量，只需read < >强urllib.request.urlopen < / >强的响应:

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

下载和保存文件最简单的方法是使用< >强urllib.request.urlretrieve < / >强函数:

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)

但请记住，urlretrieve被认为是遗产，可能会被弃用(虽然不确定原因)。

因此，最正确的的方法是使用< >强urllib.request.urlopen < / >强函数返回一个表示HTTP响应的类文件对象，并使用< >强shutil.copyfileobj < / >强将其复制到实际文件中。

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，你可能想要更简单一点，将整个下载存储在bytes对象中，然后将其写入一个文件。但这只适用于小文件。

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)

可以动态地提取.gz(可能还有其他格式)压缩数据，但这样的操作可能需要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`.
小开

我希望我正确理解了这个问题，即:当URL存储为字符串类型时，如何从服务器下载文件?

我下载文件并保存在本地使用下面的代码:

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()
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当我想要与HTTP请求相关的东西时，我使用requests包，因为它的API非常容易开始:

首先，安装requests

$ pip install requests

然后代码:

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)
小开 
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))
小开

你可以使用wget，这是一个流行的shell下载工具。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。这里有一个例子。< / p > 

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')
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这里我们可以在Python3中使用urllib的Legacy接口:

下面的函数和类是从Python 2模块urllib(而不是urllib2)移植过来的。它们在将来的某个时候可能会被弃用。

示例(2行代码):

import urllib.request


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

是的，当然requests是一个很好的包，用于与HTTP请求相关的东西。但是我们需要注意输入数据的编码类型，下面是一个解释差异的示例


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)
小开

动机

有时，我们想要得到图片，但不需要下载到真实的文件，

也就是说,下载数据并保存在内存中。

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

当我搜索一些有这些图片的网站时，我可以用模型来识别它，

我不想把这些照片存在我的磁盘驱动器上，

然后，您可以尝试以下方法来帮助您将下载数据保存在内存中。

点

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()
小开

如果你正在使用Linux，你可以通过python shell使用Linux的wget模块。下面是一个示例代码片段

import os
url = 'http://www.example.com/foo.zip'
os.system('wget %s'%url)

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