Python Assertion error even after pythonpath is set up properly

Question

I have installed virtual environment properly but it is showing me assertion error. Please help me with this I have added pythonpath also

C:\Users\welcome>pip install virtualenv<br>
Requirement already satisfied: virtualenv in d:\lib\site-packages (16.0.0)

C:\Users\welcome>cd desktop

C:\Users\welcome\Desktop>virtualenv env
Using base prefix 'd:'
Traceback (most recent call last):
  File "D:\Scripts\virtualenv-script.py", line 11, in <module>
    load_entry_point('virtualenv==1.10.1', 'console_scripts', 'virtualenv')()
  File "d:\lib\site-packages\virtualenv-1.10.1-py3.7.egg\virtualenv.py", line 821, in main
    symlink=options.symlink)
  File "d:\lib\site-packages\virtualenv-1.10.1-py3.7.egg\virtualenv.py", line 956, in create_environment
    site_packages=site_packages, clear=clear, symlink=symlink))<br>
  File "d:\lib\site-packages\virtualenv-1.10.1-py3.7.egg\virtualenv.py", line 1151, in install_python
    copy_required_modules(home_dir, symlink)
  File "d:\lib\site-packages\virtualenv-1.10.1-py3.7.egg\virtualenv.py", line 1089, in copy_required_modules
    dst_filename = change_prefix(filename, dst_prefix)<br>
  File "d:\lib\site-packages\virtualenv-1.10.1-py3.7.egg\virtualenv.py", line 1054, in change_prefix
    (filename, prefixes)
AssertionError: Filename d:\lib\os.py does not start with any of these prefixes: ['D:\\', 'D:\\']