When I want to pip something in my virtualenv, my compiler will give me an valueerror

When i want to download pymysql,flask or to check virtualenv list by “pip list” in my virtualenv, python will give me an error:

C:\Users\fzy99>workon flaskenv
(flaskenv) C:\Users\fzy99>pip install pymysql
Traceback (most recent call last):
  File "C:\Program Files\IDE_ENV\Python\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code,main_globals,None,"__main__",mod_spec)
  File "C:\Program Files\IDE_ENV\Python\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\fzy99\Envs\flaskenv\Scripts\pip.exe\__main__.py", line 4, in <module>
ValueError: source code string cannot contain null bytes

but i can download flask and pymysql to my computer when I’m not using a virtual environment.
My python version is 3.9.7

i have solved THIS problem. JUST DELET PIP.EXE IS OK!???