问题遇到的现象和发生背景
```python
(py37) C:\Users\沈仲藩>workon
Pass a name to activate one of the following virtualenvs:
==============================================================================
py37
(py37) C:\Users\沈仲藩>cd python37
(py37) C:\Users\沈仲藩\python37>mkvirtualenv -p="C:\Program Files\Python37"py37 --no-site-packages
ERROR: You must specify a name for the virtualenv