Develop Reference

pylearn2 PATH variable

there is surprisingly little documentation or tutorials about this.
I want to run pylearn2 on my Mac OSX 10.11.1.
Acoording to the tutorial I should run at first this line:
cd pylearn/pylearn2/scripts/tutorials/grbm_smd/
python make_dataset.py
Yet the script fails with this exception:
Traceback (most recent call last):
File "/Users/username/python/pylearn2/pylearn2/utils/string_utils.py", line 53, in preprocess
else os.environ[varname])
File "/Users/username/anaconda/lib/python3.4/os.py", line 633, in __getitem__
raise KeyError(key) from None
KeyError: 'PYLEARN2_DATA_PATH'
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "make_dataset.py", line 27, in <module>
train = cifar10.CIFAR10(which_set="train")
File "/Users/username/python/pylearn2/pylearn2/datasets/cifar10.py", line 71, in __init__
string_utils.preprocess('${PYLEARN2_DATA_PATH}'),
File "/Users/username/python/pylearn2/pylearn2/utils/string_utils.py", line 56, in preprocess
reraise_as(NoDataPathError())
File "/Users/username/python/pylearn2/pylearn2/utils/exc.py", line 90, in reraise_as
six.reraise(type(new_exc), new_exc, orig_exc_traceback)
File "/Users/username/anaconda/lib/python3.4/site-packages/theano/compat/six.py", line 321, in reraise
raise value.with_traceback(tb)
File "/Users/username/python/pylearn2/pylearn2/utils/string_utils.py", line 53, in preprocess
else os.environ[varname])
File "/Users/username/anaconda/lib/python3.4/os.py", line 633, in __getitem__
raise KeyError(key) from None
pylearn2.utils.exc.NoDataPathError: You need to define your PYLEARN2_DATA_PATH environment variable. If you are
using a computer at LISA, this should be set to /data/lisa/data.
Platform-specific instructions for setting environment variables:
Linux
=====
On most linux setups, you can define your environment variable by adding this
line to your ~/.bashrc file:
export PYLEARN2_VIEWER_COMMAND="eog --new-instance"
*** YOU MUST INCLUDE THE WORD "export". DO NOT JUST ASSIGN TO THE ENVIRONMENT VARIABLE ***
If you do not include the word "export", the environment variable will be set
in your bash shell, but will not be visible to processes that you launch from
it, like the python interpreter.
Don't forget that changes from your .bashrc file won't apply until you run
source ~/.bashrc
or open a new terminal window. If you're seeing this from an ipython notebook
you'll need to restart the ipython notebook, or maybe modify os.environ from
an ipython cell.
Mac OS X
========
Environment variables on Mac OS X work the same as in Linux, except you should
modify and run the "source" command on ~/.profile rather than ~/.bashrc.
Original exception:
KeyError: PYLEARN2_DATA_PATH
I inserted the following information from the exception into ~/.profile
export PYLEARN2_VIEWER_COMMAND="eog --new-instance"
and ran
source ~/.bashrc
As it still threw an exception I did some research and found out I must put the .profile file into the .bash_profile. So I added this line to .bash_profile:
#.profile
source ~/.profile
However the outcome is still the same :(
Additional information
According to the installation guide says I should add another information to the path envoirement, yet I cannot understand which in particular.
hidden files in my system
.bash_history
.bash_profile
.bash_profile-anaconda.bak
.bash_sessions
.config
.ipython
.local
.profile
.python_history
.theano
.vminfo

After going through the code myself I've found the solution. There is a bug in the sourcecode, which is missing the download_cifar10.sh script. Plus the tutorial is missing a PATH variable which is necessary.
Instruction
1.) set the PATH variable
export PYLEARN2_VIEWER_COMMAND="eog --new-instance"
export PYLEARN2_DATA_PATH=/YOURPATHTOHERE/pylearn2/datasets
2.) download cifar-10 (python version)
3.) unpack it
You will get a "cifar-10-batches-py" folder
4.) Wrap "cifar-10-batches-py" in a "cifar-10" folder
5.) Put the "cifar-10" folder into /pylearn2/datasets
The final path containing the cifar-10 files should be:
../pylearn2/datasets/cifar-10-batches-py/cifar-10
You're ready to go!

The download script exist:
https://github.com/lisa-lab/pylearn2/blob/master/pylearn2/scripts/datasets/download_cifar10.sh
Did you download Pylearn2 correctly? Did you delete files in it by mistake?

Set up multiple python installations on windows with tox

I am trying to set up tox on windows to run tests against multiple python installations. I have installed each python in folders named, C:\Python\PythonXX_YY, XX is the python version (e.g. 27) and YY is either 32 or 64. Currently, the only python in my PATH is C:\Python\Python33_64, since I use the new python launcher to run whichever version I want. I am also running tox from this version.
The first problem is that tox doesn't detect these installations, presumably because they are not in the default locations. I can get around this by setting the path in tox.ini for each environment, but it makes the setup very specific to my computer. Is there a better way of letting tox know where my pythons are globally?
The second problem is that, setting the python locations in tox.ini, I get the following error when I run it (for Python27):
Traceback (most recent call last):
File "c:\Python\Python33_64\lib\site-packages\virtualenv.py", line 2557, in <module>
main()
File "c:\Python\Python33_64\lib\site-packages\virtualenv.py", line 961, in main
never_download=options.never_download)
File "c:\Python\Python33_64\lib\site-packages\virtualenv.py", line 1062, in create_environment
site_packages=site_packages, clear=clear))
File "c:\Python\Python33_64\lib\site-packages\virtualenv.py", line 1255, in install_python
copy_required_modules(home_dir)
File "c:\Python\Python33_64\lib\site-packages\virtualenv.py", line 1193, in copy_required_modules
dst_filename = change_prefix(filename, dst_prefix)
File "c:\Python\Python33_64\lib\site-packages\virtualenv.py", line 1164, in change_prefix
(filename, prefixes)
AssertionError: Filename c:\Python\Python33_64\lib\site-packages\readline.py does not start with any of these prefixes: ['c:\\python\\python27_64']
ERROR: InvocationError: c:\python\python27_64\python.exe c:\Python\Python33_64\lib\site-packages\virtualenv.py --distribute py27 (see C:\Users\david.townshend\Documents\Global\Programming\norman\.tox\py27\log\py27-0.log)
It looks like its trying to install Python2.7 stuff from Python3.3, but I've never really used virtualenv much before so I might be mis-intepreting this error.
I'm not sure what the solution is to this, but it seems to me that the obvious solution should be for tox to use the python launcher to get the python version it needs. Is there a way to make it do this?

Looks like tox looks for pythons at such locations:
m = re.match(r"python(\d)\.(\d)", name)
if m:
# The standard names are in predictable places.
actual = r"c:\python%s%s\python.exe" % m.groups()
So you should put your pythons at c:\Python3.3\ etc. Note the dot . instead of the underscore _. Though this is a pain.

I'm not sure if Tox did this when the OP first asked the question but it seems one may now setup each environment individually as follows :
[tox]
envlist = pyw35,pyw36
skip_missing_interpreters=True
[testenv]
commands = {envpython} setup.py test
[testenv:pyw35]
basepython = C:/Python/64bit/351/python.exe
[testenv:pyw36]
basepython = C:/Python/64bit/362/python.exe
user330612 provides a variation upon this, but I personally could not get it to work.
[testenv]
commands = {envpython} setup.py test
basepython=
pyw35: C:/Python/64bit/351/python.exe
pyw36: C:/Python/64bit/362/python.exe

virtualenv on windows 7 returns AssertionError

Having trouble with virtualenv on Windows 7.
I run:
virtualenv _testenv
It returns:
Traceback (most recent call last):
File "C:\Python27\Scripts\virtualenv-script.py", line 9, in <module>
load_entry_point('virtualenv==1.5.2', 'console_scripts', 'virtualenv')()
File "C:\Python27\lib\site-packages\virtualenv.py", line 558, in main
prompt=options.prompt)
File "C:\Python27\lib\site-packages\virtualenv.py", line 647, in create_environment
site_packages=site_packages, clear=clear))
File "C:\Python27\lib\site-packages\virtualenv.py", line 771, in install_python
copy_required_modules(home_dir)
File "C:\Python27\lib\site-packages\virtualenv.py", line 725, in copy_required_modules
dst_filename = change_prefix(filename, dst_prefix)
File "C:\Python27\lib\site-packages\virtualenv.py", line 710, in change_prefix
(filename, prefixes)
AssertionError: Filename c:\Python27\Lib\os.py does not start with any of these prefixes: ['C:\\Python27']
I have the following environment variables:
PYTHONHOME=C:\Python27
PYTHONPATH=c:\Python27;c:\Python27\Lib
PYTHONSTARTUP=C:\Users\Larry\.pythonrc
PATH=%PYTHONHOME%\;%PYTHONHOME%\Scripts;etc
Installed ActiveState Python:
ActivePython 2.7.2.5 (ActiveState Software Inc.) based on
Python 2.7.2 (default, Jun 24 2011, 12:21:10) [MSC v.1500 32 bit (Intel)] on win32
I updated the PYTHONPATH=C:\Python27;C:\Python27\Lib
Still looking for a solution, I found and removed AppData/Python*. Reinstalled Python and now have a different error:
C:\xbz>virtualenv _t
PYTHONHOME is set. You *must* activate the virtualenv before using it
Overwriting _t\Lib\site.py with new content
New python executable in _t\Scripts\python2.7.exe
Not overwriting existing python script _t\Scripts\python.exe (you must use _t\Scripts\python2.7.exe)
Overwriting _t\Lib\distutils\__init__.py with new content
Installing setuptools..............
Complete output from command C:\xbz\_t\Scripts\python2.7.exe -c "#!python
\"\"\"Bootstrap setuptoo...
" --always-copy -U setuptools:
Traceback (most recent call last):
File "<string>", line 278, in <module>
File "<string>", line 210, in main
File "<string>", line 132, in download_setuptools
File "C:\Python27\Lib\urllib2.py", line 94, in <module>
import httplib
File "C:\Python27\Lib\httplib.py", line 71, in <module>
import socket
File "C:\Python27\Lib\socket.py", line 47, in <module>
import _socket
ImportError: No module named _socket
----------------------------------------
...Installing setuptools...done.
Traceback (most recent call last):
File "C:\Python27\Scripts\virtualenv-script.py", line 9, in <module>
load_entry_point('virtualenv==1.5.2', 'console_scripts', 'virtualenv')()
File "C:\Python27\lib\site-packages\virtualenv.py", line 558, in main
prompt=options.prompt)
File "C:\Python27\lib\site-packages\virtualenv.py", line 654, in create_environment
install_setuptools(py_executable, unzip=unzip_setuptools)
File "C:\Python27\lib\site-packages\virtualenv.py", line 384, in install_setuptools
_install_req(py_executable, unzip)
File "C:\Python27\lib\site-packages\virtualenv.py", line 360, in _install_req
cwd=cwd)
File "C:\Python27\lib\site-packages\virtualenv.py", line 624, in call_subprocess
% (cmd_desc, proc.returncode))
OSError: Command C:\xbz\_t\Scripts\python2.7.exe -c "#!python
\"\"\"Bootstrap setuptoo...
" --always-copy -U setuptools failed with error code 1
I hacked Lib/socket.py and inserted:
import sys
sys.path = ['', 'C:\\Python27\\lib\\site-packages\\dotcloud-0.3.1-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\dotcloud.cli-0.3.1-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\flask-0.7dev_20110622-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\werkzeug-0.6.2-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\gunicorn-0.12.2-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\wtforms-0.6.3-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\repoze.browserid-0.3-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\paste-1.7.5.1-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\django_pjax-1.0-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\paramiko-1.7.7.1-py2.7.egg', 'C:\\Python27\\lib\\site-packages\\pycrypto-2.4.1-py2.7-win32.egg', 'C:\\Python27', 'C:\\Python27\\Lib', 'C:\\Windows\\system32\\python27.zip', 'C:\\Python27\\DLLs', 'C:\\Python27\\lib\\plat-win', 'C:\\Python27\\lib\\lib-tk', 'C:\\Python27\\lib\\site-packages', 'C:\\Python27\\lib\\site-packages\\PIL', 'C:\\Python27\\lib\\site-packages\\win32', 'C:\\Python27\\lib\\site-packages\\win32\\lib', 'C:\\Python27\\lib\\site-packages\\Pythonwin', 'C:\\Python27\\lib\\site-packages\\setuptools-0.6c11-py2.7.egg-info', 'C:\\Python27\\Scripts', 'C:\\Python27\\Lib\\site-packages\\django\\bin']
Above
import _socket
The reason was that I was able to import socket from straight python prompt! So stuffed my existing path. I haven't narrowed down exactly which directory made it happy. It at least will reveal to someone else why I am getting the error without it.
Ideas? Suggestions?
Thank you. :)
I hacked Lib/socket.py and inserted:
import sys
sys.path.append('C:\\Python27\\DLLs')
Above
import _socket

3 year old question, but hopefully this answer can still help someone. Rather than setting the environment variables (which mysteriously didn't work for me), you can pass the path to your Python installation when setting up the virtual environment. In Windows, you have to path out to python.exe, but it seems that in Linux/OS X you just path to the folder. Examples:
Windows:
virtualenv -p <PATH TO PYTHON.EXE> venv
Linux/Mac:
virtualenv -p </user/path/to/python> venv
Both create a virtual environment in subfolder "venv" in current directory.

Try to set PYTHONPATH to PYTHONPATH=C:\Python27;C:\Python27\Lib (uppercase C at the start).
This can be done at the command prompt by typing set PYTHONPATH=C:\Python27;C:\Python27\Lib.
PYTHONPATH will revert back to whatever it previously was once that command prompt window is closed.

There is similar problem currently that shows error:
AssertionError: Filename C:\Python27\Lib\os.py does not start with any of
these prefixes: ['C:\\python27']
The difference is in 'C:\python27' being lower case. So the problem manifest itself in that you can not install new virtualenv or make a nested virtualenvs (we do it for testing sometimes).
The cause is in the conent of the PYTHONPATH
PYTHONPATH=C:\Python27;C:\Python27\Lib
For some reason sys.path in virtualenv.py will return c:\python27, but path to required modules will come form the PYTHONPATH and start with 'C:\Python27\Lib', hence the assertion error.
Long story short, just unset the PYTHONPATH.

For the _socket error, change your pythonpython path to:
PYTHONPATH=C:\Python27;C:\Python27\Lib;C:\Python27\DLLs

You can try the following (supppose your python is in global path):
python -m virtualenv [foldername]
This works for me, Win 10, virtualenv 15.1.0
I get it from this video, it will excute the python lib instead of calling windows exe.

I have added
if is_win:
prefixes.append('C:\PYTHON27')
to virtualenv.py and it works.

Its strange but from the error message
AssertionError: Filename c:\Python27\Lib\os.py does not start with any of these prefixes: ['C:\\Python27']
It seems, it expects the path-name for the file os.py to start with upper case 'C' and the prefix sanity check is case sensitive.
As the path to the library is derived from PYTHONPATH and in your case the drive letter is in lower case, it seems logical to change it to upper case to resolve the issue.
like
PYTHONPATH=C:\Python27;C:\Python27\Lib

I hate "summary" answers, but as I just went through a very similar issue I thought I would post my solution here as well which draws from several of these answers.
The assert error was caused because I did not have a PYTHONPATH
environment variable setup.
The socket error was caused because I did not include the
PythonXX\DLLs folder.
The full PYTHONPATH environment variable should look follows:
PYTHONPATH=C:\Python27;C:\Python27\Lib;C:\Python27\DLLs

This is an error already submitted to the Python development team: https://github.com/pypa/virtualenv/pull/697
In the meanwhile why not just change the Python installation folder name to (ptyhon27) to make the assertion work, or if you feel more confortable with that just reinstall python using the alternative location. It works with no issue.

I also ran into this problem on Windows 7. My Python27 installation was under C:\Program Files, which obviously contains a space in the path. So, on a separate Windows 7 system that did not contain Python, I did a fresh install of Python27 under C:\Python27 (the default installation path), followed by an install of setuptools (for easy_install).
Afterwards, I was able to install virtualenv CLEANLY without the above assertion error (I used easy_install).
I know that the OP's system is already using the default path, but I thought I would add my experience here as a possible solution for certain specific cases.

This issue is presumably a hangover from other more case-sensitive file systems.
Complete solution:
Read the error message from virtualenv. Remember the part where it says "does not start with any of these prefixes: ['C:\\Python27']".
Edit PYTHONPATH, or create it if you don't have one (Start+Break, Advanced system settings, Environment Variables). It shouldn't matter if it's a user variable or a system variable, unless you plan to switch user accounts.
Make the case match the error message. BOTH the drive letter AND the folder name must match (presumably intermediate folders as well, if you didn't install to C:\Python27). You can ignore the double backslash, one is fine.
The only change I made to fix the bug was as follows. The change should take effect for any new command / terminal sessions (close your open cmd.exe / powershell / etc. windows).
Old state: PYTHONPATH = C:\PYTHON27;C:\PYTHON27\LIB;C:\PYTHON27\DLLS
New state: PYTHONPATH = C:\Python27;C:\Python27\LIB;C:\Python27\DLLS
If you have any other items in your PYTHONPATH, you might as well change those too, but it probably won't affect virtualenv's ability to run.

Change "virtualenv.py" --> change_prefix with:
def change_prefix(filename, dst_prefix):
...
prefixes = sorted(prefixes, key=len, reverse=True)
filename = str(os.path.abspath(filename))[0].lower() + str(os.path.abspath(filename))[1:]
for src_prefix in prefixes:
if filename.startswith(src_prefix):
_, relpath = filename.split(src_prefix, 1)
if src_prefix != os.sep: # sys.prefix == "/"
assert relpath[0] == os.sep
relpath = relpath[1:]
return join(dst_prefix, relpath)
assert False, "Filename %s does not start with any of these prefixes: %s" % \
(filename, prefixes)
...

I had the same assertion error from a slightly different cause. The error was does not start with any of these prefixes: ['C:\\python27'] and note the lowercase "p". The actual folder names all use capital-P Python27. All the prefixes in PTYHONPATH were correct. However I had entered the PYTHONHOME variable as C:\python27 and although this was fine for Python, it caused the error in virtualenv.

Windows solution:
This is due to the difference between PYTHONPATH variable path and the one pipenv is expecting.
Suppose System Variable has below PYTHONPATH‍,
PYTHONPATH = C:\User\Bruce\AppData\Local\Programs\Python\Python37-32
And pipenv is looking for PYTHONPATH something like below:
PYTHONPATH = C:\users\bruce\appdata\local\programs\python\python37-32
Here, observe that the path text pipenv is looking has different case than what is set in System Environment variable.
To solve this issue try below steps by opening command prompt in folder where pipenv is to run:
> set PYTHONPATH=C:\users\bruce\appdata\local\programs\python\python37-32
You need to give exact same path that is shown in the AssertionError.
Then run below command to create pipenv
> pipenv install numpy
Any other library can be installed

Workaround read-only site-packages for cx_freeze

I'm currently trying to make cx_freeze to work on a Solaris workstation I have to work with, in order to make an executable from a Python script I have. Problem is, I'm not administrator of this machine, and installation of cx_freeze requests write to site-packages, which is read-only for me.
So, obviously, I get this error:
creating /usr/local/lib/python2.6/site-packages/cx_Freeze
error: could not create '/usr/local/lib/python2.6/site-packages/cx_Freeze': Read-only file system
And if I try to run it anyway, it fails:
bash-3.00$ python /home/xxxx/cx_freeze-4.2.3/cxfreeze --target-dir cx_dist src/p_tool.py
Traceback (most recent call last):
File "/home/xxxx/cx_freeze-4.2.3/cxfreeze", line 5, in <module>
main()
File "/home/xxxx/cx_freeze-4.2.3/cx_Freeze/main.py", line 187, in main
silent = options.silent)
File "/home/xxxx/cx_freeze-4.2.3/cx_Freeze/freezer.py", line 91, in __init__
self._VerifyConfiguration()
File "/home/xxxx/cx_freeze-4.2.3/cx_Freeze/freezer.py", line 371, in _VerifyConfiguration
self._GetInitScriptFileName()
File "/home/xxxx/cx_freeze-4.2.3/cx_Freeze/freezer.py", line 283, in _GetInitScriptFileName
raise ConfigError("no initscript named %s", name)
cx_Freeze.freezer.ConfigError: no initscript named Console
Obviously, this is linked to the failed installation. So, here's my question:
Without installation of virtualenv, could I avoid the writing to site-packages, and make cx_freeze to execute from my home folder?
EDIT I had a look at site.py documentation, and PYTHONPATH filling should be equivalent to use of site-packages. So my question is now more something like: what is the path to be added to PYTHONPATH, so that cx_freeze could be executed from any location?
Notes:
I would like to avoid to deal with virtualenv, as I'm already struggling to understand the executable tools...
I saw this question, but this still requires access to site-packages folder, plus it's not user-specific;
I tried adding the following path to PYTHONPATH, but this does not work: /home/xxxx/cx_freeze-4.2.3/build/lib.solaris-2.10-sun4v-2.6;
I'm also trying to use PyInstaller but have dependency problems (and the administrator is not really helping me).

This works like a charm for me :
$ python setup.py install --home=$HOME
Run in the source directory of cx_freeze found on the Sourceforge download page.

How do I work around this problem creating a virtualenv environment with a custom-build Python?

I need to run some code on a Linux machine with Python 2.3.4
pre-installed. I'm not on the sudoers list for that machine, so I
built Python 2.6.4 into (a subdirectory in) my home directory. Then I
attempted to use virtualenv (for the first time), but got:
$ Python-2.6.4/python virtualenv/virtualenv.py ENV
New python executable in ENV/bin/python
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Installing setuptools.........
Complete output from command /apps/users/dspitzer/ENV/bin/python -c "#!python
\"\"\"Bootstrap setuptoo...
" /apps/users/dspitzer/virtualen...6.egg:
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
'import site' failed; use -v for traceback
Traceback (most recent call last):
File "<string>", line 67, in <module>
ImportError: No module named md5
----------------------------------------
...Installing setuptools...done.
Traceback (most recent call last):
File "virtualenv/virtualenv.py", line 1488, in <module>
main()
File "virtualenv/virtualenv.py", line 529, in main
use_distribute=options.use_distribute)
File "virtualenv/virtualenv.py", line 619, in create_environment
install_setuptools(py_executable, unzip=unzip_setuptools)
File "virtualenv/virtualenv.py", line 361, in install_setuptools
_install_req(py_executable, unzip)
File "virtualenv/virtualenv.py", line 337, in _install_req
cwd=cwd)
File "virtualenv/virtualenv.py", line 590, in call_subprocess
% (cmd_desc, proc.returncode))
OSError: Command /apps/users/dspitzer/ENV/bin/python -c "#!python
\"\"\"Bootstrap setuptoo...
" /apps/users/dspitzer/virtualen...6.egg failed with error code 1
Should I be setting PYTHONHOME to some value? (I intentionally named
my ENV "ENV" for lack of a better name.)
Not knowing if I can ignore those errors, I tried installing nose
(0.11.1) into my ENV:
$ cd nose-0.11.1/
$ ls
AUTHORS doc/ lgpl.txt nose.egg-info/ selftest.py*
bin/ examples/ MANIFEST.in nosetests.1 setup.cfg
build/ functional_tests/ NEWS PKG-INFO setup.py
CHANGELOG install-rpm.sh* nose/ README.txt unit_tests/
$ ~/ENV/bin/python setup.py install
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Traceback (most recent call last):
File "setup.py", line 1, in <module>
from nose import __version__ as VERSION
File "/apps/users/dspitzer/nose-0.11.1/nose/__init__.py", line 1, in <module>
from nose.core import collector, main, run, run_exit, runmodule
File "/apps/users/dspitzer/nose-0.11.1/nose/core.py", line 3, in <module>
from __future__ import generators
ImportError: No module named __future__
Any advice?

Have you actually run "make install" on your custom python build? Usually you'll want to do something like
./configure --prefix=/path/to/installdir (other options)
make
make install
Note Prefix can be any directory you have full write-permissions to, for example I very often use $HOME/apps on shared-hosting environments.
Then run /path/to/installdir/bin/python, not the one from your build directory. This should create the correct variables, and after that you can install virtualenv. Might be best to install virtualenv using its setup.py:
cd virtualenv_source_dir
/path/to/installdir/bin/python setup.py install
This may require installing setuptools first, using the same method.
Then finally:
# Just to be safe
export PATH="/path/to/installdir/bin:$PATH"
virtualenv ~/ENV
~/ENV/bin/pip install somepackage # (and such)

In addition to Crast's suggestion of making sure you actually installed your custom compiled Python, you should also check that the custom Python can actually find its libraries. This is the hint you're getting with the message about PYTHONHOME. The import errors suggest you need to set in your .bashrc or appropriate shell configuration export PYTHONHOME=/path/to/python_installation.
Additionally, when you are trying to tell virtualenv to use a non-default version of python, you need to use the -p,--python flag, e.g.,
virtualenv --python=/path/to/python_installation/bin/python myenv
See also the related question, "Use different Python version with virtualenv".

I had the same error when trying to install on an existing directory that already had easy_install in lib/python2.6. I had to put a link from lib64/python2.6 to lib/python2.6.
I am not saying my fix is the right fix, rather, I'm pointing to another reason why you might get this error.

Now you can easily install Python as an unpriviledged user using Anaconda: http://continuum.io/downloads
It's similar to this question. Once of the answers details making a new environment, so you don't need to use virtual-env and avoid the occasional gotchas: Installing Anaconda into a Virtual Environment.
conda create -n myenv1 ipython scipy

I don't have enough rep to add this as a comment on #Crast's answer and this question is 4 years old, but this might be useful to someone. In Windows, you have to path out to python.exe, but it seems that in Linux/OS X you just path to the folder. Example:
Windows:
virtualenv -p <PATH TO YOUR DESIRED PYTHON.EXE> venv
Creates a virtual environment in subfolder "venv" in current directory.