Try using py -3.9 instead of python. Is D:\python\python36 in your path ?

You can use the Site-specific configuration hook.

"A path configuration file is a file whose name has the form name.pth and exists in one of the four directories mentioned above; its contents are additional items (one per line) to be added to sys.path."

In your case, you should be able to achieve what you want by simply dropping in a .pth file containing the path of the directory to include:

[root@home]$ echo "/usr/local/lib/python2.7/site-packages/" > /opt/python2.7.2/lib/python2.7/site-packages/usrlocal.pth

There are two types of site-packages directories, global and per user.

1. Global site-packages ("dist-packages") directories are listed in sys.path when you run:

    python -m site
   

   For a more concise list run getsitepackages from the site module in Python code:

    python -c 'import site; print(site.getsitepackages())'
   

   Caution: In virtual environments getsitepackages is not available with older versions of virtualenv, sys.path from above will list the virtualenv's site-packages directory correctly, though. In Python 3, you may use the sysconfig module instead:

    python3 -c 'import sysconfig; print(sysconfig.get_paths()["purelib"])'
   

2. The per user site-packages directory (PEP 370) is where Python installs your local packages:

    python -m site --user-site
   

   If this points to a non-existing directory check the exit status of Python and see python -m site --help for explanations.

   Hint: Running pip list --user or pip freeze --user gives you a list of all installed per user site-packages.

Practical Tips

• <package>.__path__ lets you identify the location(s) of a specific package: (details)

    $ python -c "import setuptools as _; print(_.__path__)"
    ['/usr/lib/python2.7/dist-packages/setuptools']
  

• <module>.__file__ lets you identify the location of a specific module: (difference)

    $ python3 -c "import os as _; print(_.__file__)"
    /usr/lib/python3.6/os.py
  

• Run pip show <package> to show Debian-style package information:

    $ pip show pytest
    Name: pytest
    Version: 3.8.2
    Summary: pytest: simple powerful testing with Python
    Home-page: https://docs.pytest.org/en/latest/
    Author: Holger Krekel, Bruno Oliveira, Ronny Pfannschmidt, Floris Bruynooghe, Brianna Laugher, Florian Bruhin and others
    Author-email: None
    License: MIT license
    Location: /home/peter/.local/lib/python3.4/site-packages
    Requires: more-itertools, atomicwrites, setuptools, attrs, pathlib2, six, py, pluggy
  

easy_install should install the packages in the Python installation's site-packages directory. It could have happened that you changed Python's directory accidentally. Reinstalling easy_install should fix this.

Otherwise you could use:easy_install --install-dir C:\Python27\Lib\site-packages\Lib\site-packages\ django-piston

However, this last option has two issues:

1. Make sure C:\Python27\Lib\site-packages\Lib\site-packages\ is in PYTHONPATH
2. You will need to indicate a install-dir directory for every new package you install

site-packages is the target directory of manually built Python packages. When you build and install Python packages from source (using distutils, probably by executing python setup.py install), you will find the installed modules in site-packages by default.

There are standard locations:

• Unix (pure)¹: prefix/lib/pythonX.Y/site-packages
• Unix (non-pure): exec-prefix/lib/pythonX.Y/site-packages
• Windows: prefix\Lib\site-packages

¹ Pure means that the module uses only Python code. Non-pure can contain C/C++ code as well.

site-packages is by default part of the Python search path, so modules installed there can be imported easily afterwards.

Useful reading

• Installing Python Modules (for Python 2)
• Installing Python Modules (for Python 3)