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A script which demonstrates how to extend Python 3.3's EnvBuilder, by installing setuptools and pip in created venvs. This functionality is not provided as an integral part of Python 3.3 because, while setuptools and pip are very popular, they are third-party packages. The script needs Python 3.3 or later; invoke it using "python -h"…
# Copyright (C) 2013 Vinay Sajip. New BSD License.
import os
import os.path
from subprocess import Popen, PIPE
import sys
from threading import Thread
from urllib.parse import urlparse
from urllib.request import urlretrieve
import venv
class ExtendedEnvBuilder(venv.EnvBuilder):
This builder installs setuptools and pip so that you can pip or
easy_install other packages into the created environment.
:param nodist: If True, setuptools and pip are not installed into the
created environment.
:param nopip: If True, pip is not installed into the created
:param progress: If setuptools or pip are installed, the progress of the
installation can be monitored by passing a progress
callable. If specified, it is called with two
arguments: a string indicating some progress, and a
context indicating where the string is coming from.
The context argument can have one of three values:
'main', indicating that it is called from virtualize()
itself, and 'stdout' and 'stderr', which are obtained
by reading lines from the output streams of a subprocess
which is used to install the app.
If a callable is not specified, default progress
information is output to sys.stderr.
def __init__(self, *args, **kwargs):
self.nodist = kwargs.pop('nodist', False)
self.nopip = kwargs.pop('nopip', False)
self.progress = kwargs.pop('progress', None)
self.verbose = kwargs.pop('verbose', False)
super().__init__(*args, **kwargs)
def post_setup(self, context):
Set up any packages which need to be pre-installed into the
environment being created.
:param context: The information for the environment creation request
being processed.
os.environ['VIRTUAL_ENV'] = context.env_dir
if not self.nodist:
# Can't install pip without setuptools
if not self.nopip and not self.nodist:
def reader(self, stream, context):
Read lines from a subprocess' output stream and either pass to a progress
callable (if specified) or write progress information to sys.stderr.
progress = self.progress
while True:
s = stream.readline()
if not s:
if progress is not None:
progress(s, context)
if not self.verbose:
def install_script(self, context, name, url):
_, _, path, _, _, _ = urlparse(url)
fn = os.path.split(path)[-1]
binpath = context.bin_path
distpath = os.path.join(binpath, fn)
# Download script into the env's binaries folder
urlretrieve(url, distpath)
progress = self.progress
if self.verbose:
term = '\n'
term = ''
if progress is not None:
progress('Installing %s ...%s' % (name, term), 'main')
sys.stderr.write('Installing %s ...%s' % (name, term))
# Install in the env
args = [context.env_exe, fn]
p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
if progress is not None:
progress('done.', 'main')
# Clean up - no longer needed
def install_setuptools(self, context):
Install setuptools in the environment.
:param context: The information for the environment creation request
being processed.
url = ''
self.install_script(context, 'setuptools', url)
# clear up the setuptools archive which gets downloaded
pred = lambda o: o.startswith('setuptools-') and o.endswith('.tar.gz')
files = filter(pred, os.listdir(context.bin_path))
for f in files:
f = os.path.join(context.bin_path, f)
def install_pip(self, context):
Install pip in the environment.
:param context: The information for the environment creation request
being processed.
url = ''
self.install_script(context, 'pip', url)
def main(args=None):
compatible = True
if sys.version_info < (3, 3):
compatible = False
elif not hasattr(sys, 'base_prefix'):
compatible = False
if not compatible:
raise ValueError('This script is only for use with '
'Python 3.3 or later')
import argparse
parser = argparse.ArgumentParser(prog=__name__,
description='Creates virtual Python '
'environments in one or '
'more target '
parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
help='A directory to create the environment in.')
parser.add_argument('--no-setuptools', default=False,
action='store_true', dest='nodist',
help="Don't install setuptools or pip in the "
"virtual environment.")
parser.add_argument('--no-pip', default=False,
action='store_true', dest='nopip',
help="Don't install pip in the virtual "
parser.add_argument('--system-site-packages', default=False,
action='store_true', dest='system_site',
help='Give the virtual environment access to the '
'system site-packages dir.')
if == 'nt':
use_symlinks = False
use_symlinks = True
parser.add_argument('--symlinks', default=use_symlinks,
action='store_true', dest='symlinks',
help='Try to use symlinks rather than copies, '
'when symlinks are not the default for '
'the platform.')
parser.add_argument('--clear', default=False, action='store_true',
dest='clear', help='Delete the contents of the '
'environment directory if it '
'already exists, before '
'environment creation.')
parser.add_argument('--upgrade', default=False, action='store_true',
dest='upgrade', help='Upgrade the environment '
'directory to use this version '
'of Python, assuming Python '
'has been upgraded in-place.')
parser.add_argument('--verbose', default=False, action='store_true',
dest='verbose', help='Display the output '
'from the scripts which '
'install setuptools and pip.')
options = parser.parse_args(args)
if options.upgrade and options.clear:
raise ValueError('you cannot supply --upgrade and --clear together.')
builder = ExtendedEnvBuilder(system_site_packages=options.system_site,
for d in options.dirs:
if __name__ == '__main__':
rc = 1
rc = 0
except Exception as e:
print('Error: %s' % e, file=sys.stderr)
dotysan commented Sep 15, 2013

Hi, and thanks!

I'm fiddling with a Python-from-scratch script...and found that your venv wrapper doesn't generate an error whenever pip install fails due to a missing bz2 library.

+ set -e
+ $HOME/bin/python3.3 foo
Installing setuptools ....................................................................................................................................................................................................................................................done.
Installing pip .........done.
+ echo DONE

Bit pip is not installed!

If I add --verbose, it reveals the error. And of course the workaround is to build Python with bzip2 support. But still no exit(!0) status.

abbottc commented Nov 9, 2013

I found that (on Linux) pip installs to the "local/bin" folder of the venv. But since running "activate" only prepends the "bin" folder to $PATH, a symlink needs to be created so that pip can be run in the venv without specifying a path. I forked your code and added a few lines to do this. If you want to pull the changes, it's here:

And thanks for the script!

Yajo commented Nov 15, 2013

Quick shortcut for using:

$ python3 -c "$(curl" env-dir

As mentioned, I needed to install bzip2 $ pip3 install bz2file.

I installed without symlinks, but core modules are missing, like os, encodings...

$ ./pyvenvex-env/bin/python3.4
Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
[GCC 4.8.2] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os
<module 'os' from '/usr/lib/python3.4/'>

@vsajip I forked and made some cosmetic changes to this script that I would like to include in an update to the Python docs:

I don't know how to submit PRs to gists, so hopefully you can just copy-pasta.

Python docs:

Issue tracker:

These changes help to clarify that a "virtual environment" (and not an "env" or "environment") is being built. Thank you for your consideration.

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