Question: running the following command

```
virtualenv -p /usr/local/bin/pypy pypy

```

exits with error like

```
Running virtualenv with interpreter /usr/local/bin/pypy
New pypy executable in pypy/bin/pypy
debug: WARNING: Library path not found, using compiled-in sys.path.
debug: WARNING: 'sys.prefix' will not be set.
debug: WARNING: Make sure the pypy binary is kept inside its tree of files.
debug: WARNING: It is ok to create a symlink to it from somewhere else.
'import site' failed
AttributeError: 'module' object has no attribute 'prefix'
ERROR: The executable pypy/bin/pypy is not functioning
ERROR: It thinks sys.prefix is u'/Users/myname' (should be u'/Users/myname/pypy')
ERROR: virtualenv is not compatible with this system or executable

```

I'm running Mac OS X 10.8.1 (Mountain Lion) with CPython 2.7.3 and installed pypy 1.9 using Brew. virtualenv's version is 1.8.4

Using pre-built pypy binary for Mac OS X downloaded directly from pypy's website doesn't make any difference

Answer: 
For `windows` this worked for me :

```py

python -m virtualenv -p <Your PYPY installed path\pypy3.exe> <venv_name>

```
With pypy-4.0.1 and virtualenv 14.0.3, out of the box I get an error:

```
Q:\>c:\pypy\bin\virtualenv -p c:\pypy\pypy.exe my_pypy_virtualenv
Already using interpreter c:\pypy\pypy.exe
New pypy executable in Q:\my_pypy_virtualenv\bin\pypy.exe
debug: OperationError:
debug:  operror-type: ImportError
debug:  operror-value: No module named UserDict
ERROR: The executable Q:\my_pypy_virtualenv\bin\pypy.exe is not functioning
ERROR: It thinks sys.prefix is u'q:\\' (should be u'q:\\my_pypy_virtualenv')
ERROR: virtualenv is not compatible with this system or executable
Note: some Windows users have reported this error when they installed Python for "Only this user" or have multiple versions of Python installed. Copying the appropriate PythonXX.dll to the virtualenv Scripts/ directory may fix this problem.

```

Searching the original pypy install for `UserDict*`, I found `UserDict.py` in `lib-python\2.7` but in the virtualenv's `lib-python\2.7` there was only `userdict.py` and none of the capitalized `User` files. Following the example of the other solutions, I removed the virtualenv's `userdict.py` and copied the original `User*` files, and reran the `virtualenv` command, and it ran without error.