使用pip install virtualenv 之后，试图通过 virtualenv --no-download myenv 创建一个python的虚拟环境
但是出现了一个问题，在最后一行报一个错：
...Installing setuptools, pip, wheel...done.
Traceback (most recent call last):
File "c:\python\lib\runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "c:\python\lib\runpy.py", line 85, in _run_code
exec(code, run_globals)
File "C:\python\Scripts\virtualenv.exe\__main__.py", line 9, in <module>
File "c:\python\lib\site-packages\virtualenv.py", line 793, in main
symlink=options.symlink,
File "c:\python\lib\site-packages\virtualenv.py", line 1088, in create_environment
install_wheel(to_install, py_executable, search_dirs, download=download)
File "c:\python\lib\site-packages\virtualenv.py", line 935, in install_wheel
_install_wheel_with_search_dir(download, project_names, py_executable, search_dirs)
File "c:\python\lib\site-packages\virtualenv.py", line 1025, in _install_wheel_with_search_dir
call_subprocess(cmd, show_stdout=False, extra_env=env, stdin=script)
File "c:\python\lib\site-packages\virtualenv.py", line 886, in call_subprocess
raise OSError("Command {} failed with error code {}".format(cmd_desc, proc.returncode))
OSError: Command C:\Users\hwj71\mypro...v\Scripts\python.exe - setuptools pip wheel failed with error code 2
显然，这种错误是无法定位的，只能往前找，直到找到这句话：
Error("HTTPSConnectionPool(host='pypi.org', port=443): Read timed out. (read timeout=15)",)'
哦！才明白，原来是多次请求这个 pypi.org 网址超时出现的问题，赶紧使用网页浏览器来试一下，果然！只能使出我的绝招，通过一翻努力，当使用网页可以浏览到的时候，再执行：
virtualenv --no-download myenv
结果：
Using base prefix 'c:\\python'
New python executable in C:\Users\hwj71\myproject\venv\Scripts\python.exe
Installing setuptools, pip, wheel...
done.
大喜！所以，遇到问题的时候要一步一步的去找，问题总会解决的
