virtualenv [OPTIONS] ENV_DIR
ENV_DIRis an absolute or relative path to a directory to create the virtual environment in.
show program’s version number and exit
show this help message and exit
The Python interpreter to use, e.g.,
--python=python2.5will use the python2.5 interpreter to create the new environment. The default is the interpreter that virtualenv was installed with (like
Clear out the non-root install and start from scratch.
Give the virtual environment access to the global site-packages.
Always copy files rather than symlinking.
Make an EXISTING virtualenv environment relocatable. This fixes up scripts and makes all .pth files relative.
Unzip Setuptools when installing it.
Do not install setuptools in the new virtualenv.
Do not install pip in the new virtualenv.
Do not install wheel in the new virtualenv.
Directory to look for setuptools/pip distributions in. This option can be specified multiple times.
Provides an alternative prompt prefix for this environment.
Download preinstalled packages from PyPI.
Do not download preinstalled packages from PyPI.
DEPRECATED. Retained only for backward compatibility. Not having access to global site-packages is now the default behavior.
Each command line option is automatically used to look for environment
variables with the name format
VIRTUALENV_<UPPER_NAME>. That means
the name of the command line options are capitalized and have dashes
'-') replaced with underscores (
For example, to automatically use a custom Python binary instead of the one virtualenv is run with you can also set an environment variable:
$ export VIRTUALENV_PYTHON=/opt/python-3.3/bin/python $ virtualenv ENV
It’s the same as passing the option to virtualenv directly:
$ virtualenv --python=/opt/python-3.3/bin/python ENV
This also works for appending command line options, like
Just leave an empty space between the passed values, e.g.:
$ export VIRTUALENV_EXTRA_SEARCH_DIR="/path/to/dists /path/to/other/dists" $ virtualenv ENV
is the same as calling:
$ virtualenv --extra-search-dir=/path/to/dists --extra-search-dir=/path/to/other/dists ENV
virtualenv also looks for a standard ini config file. On Unix and Mac OS X
$HOME/.virtualenv/virtualenv.ini and on Windows, it’s
The names of the settings are derived from the long command line option,
e.g. the option
--python would look like this:
[virtualenv] python = /opt/python-3.3/bin/python
Appending options like
--extra-search-dir can be written on multiple
[virtualenv] extra-search-dir = /path/to/dists /path/to/other/dists
Please have a look at the output of
--help for a full list
of supported options.
Creating Your Own Bootstrap Scripts¶
While this creates an environment, it doesn’t put anything into the environment. Developers may find it useful to distribute a script that sets up a particular environment, for example a script that installs a particular web application.
A bootstrap script requires a
virtualenv_support directory containing
setuptools wheels alongside it, just like the actual virtualenv
script. Running a bootstrap script without a
is unsupported (but if you use
--no-setuptools and manually install
setuptools in your virtualenv, it will work).
To create a script like this, call
virtualenv.create_bootstrap_script(), and write the
result to your new bootstrapping script.
Creates a bootstrap script from
extra_text, which is like this script but with extend_parser, adjust_options, and after_install hooks.
This returns a string that (written to disk of course) can be used as a bootstrap script with your own customizations. The script will be the standard virtualenv.py script, with your extra text added (your extra text should be Python code).
If you include these functions, they will be called:
You can add or remove options from the parser here.
You can change options here, or change the args (if you accept different kinds of arguments, be sure you modify
argsso it is only
After everything is installed, this function is called. This is probably the function you are most likely to use. An example would be:
def after_install(options, home_dir): if sys.platform == 'win32': bin = 'Scripts' else: bin = 'bin' subprocess.call([join(home_dir, bin, 'easy_install'), 'MyPackage']) subprocess.call([join(home_dir, bin, 'my-package-script'), 'setup', home_dir])
This example immediately installs a package, and runs a setup script from that package.
Here’s a more concrete example of how you could use this:
import virtualenv, textwrap output = virtualenv.create_bootstrap_script(textwrap.dedent(""" import os, subprocess def after_install(options, home_dir): etc = join(home_dir, 'etc') if not os.path.exists(etc): os.makedirs(etc) subprocess.call([join(home_dir, 'bin', 'easy_install'), 'BlogApplication']) subprocess.call([join(home_dir, 'bin', 'paster'), 'make-config', 'BlogApplication', join(etc, 'blog.ini')]) subprocess.call([join(home_dir, 'bin', 'paster'), 'setup-app', join(etc, 'blog.ini')]) """)) f = open('blog-bootstrap.py', 'w').write(output)
Another example is available here.
Compatibility with the stdlib venv module¶
Starting with Python 3.3, the Python standard library includes a
module that provides similar functionality to
virtualenv - however, the
mechanisms used by the two modules are very different.
Problems arise when environments get “nested” (a virtual environment is created from within another one - for example, running the virtualenv tests using tox, where tox creates a virtual environment to run the tests, and the tests themselves create further virtual environments).
virtualenv supports creating virtual environments from within another one
sys.real_prefix variable allows
virtualenv to locate the “base”
environment) but stdlib-style
venv environments don’t use that mechanism,
so explicit support is needed for those environments.
A standard library virtual environment is most easily identified by checking
sys.base_prefix. If these differ, the interpreter is
running in a virtual environment and the base interpreter is located in the
directory specified by
sys.base_prefix. Therefore, when
sys.base_prefix is set, virtualenv gets the interpreter files from there
rather than from
sys.prefix (in the same way as
used for virtualenv-style environments). In practice, this is sufficient for
all platforms other than Windows.
On Windows from Python 3.7.2 onwards, a stdlib-style virtual environment does
not contain an actual Python interpreter executable, but rather a “redirector”
which launches the actual interpreter from the base environment (this
redirector is based on the same code as the standard
py.exe launcher). As
a result, the virtualenv approach of copying the interpreter from the starting
environment fails. In order to correctly set up the virtualenv, therefore, we
need to be running from a “full” environment. To ensure that, we re-invoke the
virtualenv.py script using the “base” interpreter, in the same way as we
do with the
--python command line option.
The process of identifying the base interpreter is complicated by the fact that the implementation changed between different Python versions. The logic used is as follows:
- If the (private) attribute
sys._base_executableis present, this is the base interpreter. This is the long-term solution and should be stable in the future (the attribute may become public, and have the leading underscore removed, in a Python 3.8, but that is not confirmed yet).
- In the absence of
sys._base_executable(only the case for Python 3.7.2) we check for the existence of the environment variable
__PYVENV_LAUNCHER__. This is used by the redirector, and if it is present, we know that we are in a stdlib-style virtual environment and need to locate the base Python. In most cases, the base environment is located at
sys.base_prefix- however, in the case where the user creates a virtualenv, and then creates a venv from that virtualenv,
sys.base_prefixis not correct - in that case, though, we have
sys.real_prefix(set by virtualenv) which is correct.
There is one further complication - as noted above, the environment variable
__PYVENV_LAUNCHER__ affects how the interpreter works, so before we
re-invoke the virtualenv script, we remove this from the environment.