$ pex --version
2.1.110

$ python3 -c 'import attr' 
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ModuleNotFoundError: No module named 'attr'

$ pex -o psutil.pex --layout=loose 'psutil'  

$ python3
Python 3.9.4 (default, Apr 15 2021, 21:01:17) 
[Clang 12.0.0 (clang-1200.0.32.29)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
(ins)>>> import sys
(ins)>>> sys.path.append('./psutil.pex')
(ins)>>> import __pex__
(ins)>>> import attr
(ins)>>> attr
<module 'pex.vendor._vendored.attrs.attr' from '/Users/zmanji/tmp/psutil.pex/.bootstrap/pex/vendor/_vendored/attrs/attr/__init__.py'>