初次安装python3.8后，使用py抓取网页，代码中会使用
import requests
...
运行代码会提示
ModuleNotFoundError: No module named 'requests'
问题：因为你的python还未安装requests库，需要通过pip安装。
(venv) E:\dev\uspider>pip install requests
Collecting requests
Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ConnectTimeoutError(<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x0000021F85E8A760
>, 'Connection to pypi.org timed out. (connect timeout=15)')': /simple/requests/
Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ConnectTimeoutError(<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x0000021F85E8A340
>, 'Connection to pypi.org timed out. (connect timeout=15)')': /simple/requests/
Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ConnectTimeoutError(<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x0000021F85EACDC0
>, 'Connection to pypi.org timed out. (connect timeout=15)')': /simple/requests/
Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ConnectTimeoutError(<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x0000021F85EACAC0
>, 'Connection to pypi.org timed out. (connect timeout=15)')': /simple/requests/
Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'ConnectTimeoutError(<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x0000021F85EAC610
>, 'Connection to pypi.org timed out. (connect timeout=15)')': /simple/requests/
Could not find a version that satisfies the requirement requests (from versions: )
No matching distribution found for requests
从执行的过程来看，请求一直处于超时。这是由于国内很多情况下，无法正常去下载国外服务器资源导致。
解决方法：使用国内镜像，常用的有镜像有
- 清华大学镜像：https://pypi.tuna.tsinghua.edu.cn/simple/
- 阿里云：https://mirrors.aliyun.com/pypi/simple/
- 中科大镜像：https://pypi.mirrors.ustc.edu.cn/simple/
- 豆瓣镜像：https://pypi.douban.com/simple/
- 中科大镜像2：https://pypi.mirrors.ustc.edu.cn/simple/
使用镜像的安装范式为：
pip install xxxx -i http://… 或者 pip install -i https://… xxxx。
# 示例如下：
pip install requests -i https://mirrors.aliyun.com/pypi/simple/
注意：如果安装过程中提示需要升级pip
You should consider upgrading via the 'python -m pip install --upgrade pip' command.
# 解决命令
python -m pip install --upgrade pip -i http://mirrors.aliyun.com/pypi/simple/
当安装完requests后，测试通过，OK！
>>>
>>> import requests
>>>
