venv
— 虚拟环境的创建
¶
3.3 版新增。
源代码： Lib/venv/
venv
module provides support for creating lightweight “virtual environments” with their own site directories, optionally isolated from system site directories. Each virtual environment has its own Python binary (allowing creation of environments with various Python versions) and can have its own independent set of installed Python packages in its site directories.
见 PEP 405 for more information about Python virtual environments.
注意
pyvenv
script has been deprecated as of Python 3.6 in favor of using
python3
-m
venv
to help prevent any potential confusion as to which Python interpreter a virtual environment will be based on.
Creation of
虚拟环境
is done by executing the command
venv
:
python3 -m venv /path/to/new/virtual/environment
Running this command creates the target directory (creating any parent directories that don’t exist already) and places a
pyvenv.cfg
file in it with a
home
key pointing to the Python installation from which the command was run. It also creates a
bin
(或
脚本
on Windows) subdirectory containing a copy/symlink of the Python binary/binaries (as appropriate for the platform or arguments used at environment creation time). It also creates an (initially empty)
lib/pythonX.Y/site-packages
subdirectory (on Windows, this is
Lib\site-packages
). If an existing directory is specified, it will be re-used.
从 3.6 版起弃用：
pyvenv
was the recommended tool for creating virtual environments for Python 3.3 and 3.4, and is
deprecated in Python 3.6
.
3.5 版改变：
The use of
venv
is now recommended for creating virtual environments.
On Windows, invoke the
venv
command as follows:
c:\>c:\Python35\python -m venv c:\path\to\myenv
Alternatively, if you configured the
PATH
and
PATHEXT
variables for your
Python installation
:
c:\>python -m venv c:\path\to\myenv
The command, if run with
-h
, will show the available options:
usage: venv [-h] [--system-site-packages] [--symlinks | --copies] [--clear]
[--upgrade] [--without-pip]
ENV_DIR [ENV_DIR ...]
Creates virtual Python environments in one or more target directories.
positional arguments:
ENV_DIR A directory to create the environment in.
optional arguments:
-h, --help show this help message and exit
--system-site-packages
Give the virtual environment access to the system
site-packages dir.
--symlinks Try to use symlinks rather than copies, when symlinks
are not the default for the platform.
--copies Try to use copies rather than symlinks, even when
symlinks are the default for the platform.
--clear Delete the contents of the environment directory if it
already exists, before environment creation.
--upgrade Upgrade the environment directory to use this version
of Python, assuming Python has been upgraded in-place.
--without-pip Skips installing or upgrading pip in the virtual
environment (pip is bootstrapped by default)
Once an environment has been created, you may wish to activate it, e.g. by
sourcing an activate script in its bin directory.
3.4 版改变：
Installs pip by default, added the
--without-pip
and
--copies
选项
3.4 版改变：
In earlier versions, if the target directory already existed, an error was raised, unless the
--clear
or
--upgrade
option was provided.
The created
pyvenv.cfg
file also includes the
include-system-site-packages
key, set to
true
if
venv
is run with the
--system-site-packages
option,
false
否则。
Unless the
--without-pip
option is given,
ensurepip
will be invoked to bootstrap
pip
into the virtual environment.
Multiple paths can be given to
venv
, in which case an identical virtual environment will be created, according to the given options, at each provided path.
Once a virtual environment has been created, it can be “activated” using a script in the virtual environment’s binary directory. The invocation of the script is platform-specific ( <venv> must be replaced by the path of the directory containing the virtual environment):
| 平台 | Shell | Command to activate virtual environment |
|---|---|---|
| Posix | bash/zsh | $ source <venv>/bin/activate |
| fish | $ . <venv>/bin/activate.fish | |
| csh/tcsh | $ source <venv>/bin/activate.csh | |
| Windows | cmd.exe | C:\> <venv>\Scripts\activate.bat |
| PowerShell | PS C:\> <venv>\Scripts\Activate.ps1 |
You don’t specifically need to activate an environment; activation just prepends the virtual environment’s binary directory to your path, so that “python” invokes the virtual environment’s Python interpreter and you can run installed scripts without having to use their full path. However, all scripts installed in a virtual environment should be runnable without activating it, and run with the virtual environment’s Python automatically.
You can deactivate a virtual environment by typing “deactivate” in your shell. The exact mechanism is platform-specific: for example, the Bash activation script defines a “deactivate” function, whereas on Windows there are separate scripts called
deactivate.bat
and
Deactivate.ps1
which are installed when the virtual environment is created.
3.4 版新增：
fish
and
csh
activation scripts.
注意
A virtual environment is a Python environment such that the Python interpreter, libraries and scripts installed into it are isolated from those installed in other virtual environments, and (by default) any libraries installed in a “system” Python, i.e., one which is installed as part of your operating system.
A virtual environment is a directory tree which contains Python executable files and other files which indicate that it is a virtual environment.
Common installation tools such as
Setuptools
and
pip
work as expected with virtual environments. In other words, when a virtual environment is active, they install Python packages into the virtual environment without needing to be told to do so explicitly.
When a virtual environment is active (i.e., the virtual environment’s Python interpreter is running), the attributes
sys.prefix
and
sys.exec_prefix
point to the base directory of the virtual environment, whereas
sys.base_prefix
and
sys.base_exec_prefix
point to the non-virtual environment Python installation which was used to create the virtual environment. If a virtual environment is not active, then
sys.prefix
如同
sys.base_prefix
and
sys.exec_prefix
如同
sys.base_exec_prefix
(they all point to a non-virtual environment Python installation).
When a virtual environment is active, any options that change the installation path will be ignored from all distutils configuration files to prevent projects being inadvertently installed outside of the virtual environment.
When working in a command shell, users can make a virtual environment active by running an
activate
script in the virtual environment’s executables directory (the precise filename is shell-dependent), which prepends the virtual environment’s directory for executables to the
PATH
environment variable for the running shell. There should be no need in other circumstances to activate a virtual environment—scripts installed into virtual environments have a “shebang” line which points to the virtual environment’s Python interpreter. This means that the script will run with that interpreter regardless of the value of
PATH
. On Windows, “shebang” line processing is supported if you have the Python Launcher for Windows installed (this was added to Python in 3.3 - see
PEP 397
for more details). Thus, double-clicking an installed script in a Windows Explorer window should run the script with the correct interpreter without there needing to be any reference to its virtual environment in
PATH
.
The high-level method described above makes use of a simple API which provides mechanisms for third-party virtual environment creators to customize environment creation according to their needs, the
EnvBuilder
类。
venv.
EnvBuilder
(
system_site_packages=False
,
clear=False
,
symlinks=False
,
upgrade=False
,
with_pip=False
,
prompt=None
)
¶
EnvBuilder
class accepts the following keyword arguments on instantiation:
system_site_packages
– a Boolean value indicating that the system Python site-packages should be available to the environment (defaults to
False
).
clear
– a Boolean value which, if true, will delete the contents of any existing target directory, before creating the environment.
symlinks
– a Boolean value indicating whether to attempt to symlink the Python binary (and any necessary DLLs or other binaries, e.g.
pythonw.exe
), rather than copying.
upgrade
– a Boolean value which, if true, will upgrade an existing environment with the running Python - for use when that Python has been upgraded in-place (defaults to
False
).
with_pip
– a Boolean value which, if true, ensures pip is installed in the virtual environment. This uses
ensurepip
采用
--default-pip
选项。
prompt
– a String to be used after virtual environment is activated (defaults to
None
which means directory name of the environment would be used).
3.4 版改变：
添加
with_pip
parameter
3.6 版新增：
添加
prompt
parameter
Creators of third-party virtual environment tools will be free to use the provided
EnvBuilder
class as a base class.
The returned env-builder is an object which has a method,
create
:
create
(
env_dir
)
¶
This method takes as required argument the path (absolute or relative to the current directory) of the target directory which is to contain the virtual environment. The
create
method will either create the environment in the specified directory, or raise an appropriate exception.
create
方法在
EnvBuilder
class illustrates the hooks available for subclass customization:
def create(self, env_dir):
"""
Create a virtualized Python environment in a directory.
env_dir is the target directory to create an environment in.
"""
env_dir = os.path.abspath(env_dir)
context = self.ensure_directories(env_dir)
self.create_configuration(context)
self.setup_python(context)
self.setup_scripts(context)
self.post_setup(context)
Each of the methods
ensure_directories()
,
create_configuration()
,
setup_python()
,
setup_scripts()
and
post_setup()
can be overridden.
ensure_directories
(
env_dir
)
¶
Creates the environment directory and all necessary directories, and returns a context object. This is just a holder for attributes (such as paths), for use by the other methods. The directories are allowed to exist already, as long as either
clear
or
upgrade
were specified to allow operating on an existing environment directory.
create_configuration
(
context
)
¶
Creates the
pyvenv.cfg
configuration file in the environment.
setup_python
(
context
)
¶
Creates a copy of the Python executable (and, under Windows, DLLs) in the environment. On a POSIX system, if a specific executable
python3.x
was used, symlinks to
python
and
python3
will be created pointing to that executable, unless files with those names already exist.
setup_scripts
(
context
)
¶
Installs activation scripts appropriate to the platform into the virtual environment.
post_setup
(
context
)
¶
A placeholder method which can be overridden in third party implementations to pre-install packages in the virtual environment or perform other post-creation steps.
此外，
EnvBuilder
provides this utility method that can be called from
setup_scripts()
or
post_setup()
in subclasses to assist in installing custom scripts into the virtual environment.
install_scripts
(
context
,
path
)
¶
path
is the path to a directory that should contain subdirectories “common”, “posix”, “nt”, each containing scripts destined for the bin directory in the environment. The contents of “common” and the directory corresponding to
os.name
are copied after some text replacement of placeholders:
__VENV_DIR__
is replaced with the absolute path of the environment directory.
__VENV_NAME__
is replaced with the environment name (final path segment of environment directory).
__VENV_PROMPT__
is replaced with the prompt (the environment name surrounded by parentheses and with a following space)
__VENV_BIN_NAME__
is replaced with the name of the bin directory (either
bin
or
脚本
).
__VENV_PYTHON__
is replaced with the absolute path of the environment’s executable.
The directories are allowed to exist (for when an existing environment is being upgraded).
There is also a module-level convenience function:
venv.
create
(
env_dir
,
system_site_packages=False
,
clear=False
,
symlinks=False
,
with_pip=False
)
¶
创建
EnvBuilder
with the given keyword arguments, and call its
create()
method with the
env_dir
自变量。
3.4 版改变：
添加
with_pip
parameter
EnvBuilder
¶
The following script shows how to extend
EnvBuilder
by implementing a subclass which installs setuptools and pip into a created virtual environment:
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 virtual environment.
:param nodist: If True, setuptools and pip are not installed into the
created virtual environment.
:param nopip: If True, pip is not installed into the created
virtual environment.
: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
virtual environment being created.
:param context: The information for the virtual environment
creation request being processed.
"""
os.environ['VIRTUAL_ENV'] = context.env_dir
if not self.nodist:
self.install_setuptools(context)
# Can't install pip without setuptools
if not self.nopip and not self.nodist:
self.install_pip(context)
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:
break
if progress is not None:
progress(s, context)
else:
if not self.verbose:
sys.stderr.write('.')
else:
sys.stderr.write(s.decode('utf-8'))
sys.stderr.flush()
stream.close()
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 virtual environment's binaries folder
urlretrieve(url, distpath)
progress = self.progress
if self.verbose:
term = '\n'
else:
term = ''
if progress is not None:
progress('Installing %s ...%s' % (name, term), 'main')
else:
sys.stderr.write('Installing %s ...%s' % (name, term))
sys.stderr.flush()
# Install in the virtual environment
args = [context.env_exe, fn]
p = Popen(args, stdout=PIPE, stderr=PIPE, cwd=binpath)
t1 = Thread(target=self.reader, args=(p.stdout, 'stdout'))
t1.start()
t2 = Thread(target=self.reader, args=(p.stderr, 'stderr'))
t2.start()
p.wait()
t1.join()
t2.join()
if progress is not None:
progress('done.', 'main')
else:
sys.stderr.write('done.\n')
# Clean up - no longer needed
os.unlink(distpath)
def install_setuptools(self, context):
"""
Install setuptools in the virtual environment.
:param context: The information for the virtual environment
creation request being processed.
"""
url = 'https://bitbucket.org/pypa/setuptools/downloads/ez_setup.py'
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)
os.unlink(f)
def install_pip(self, context):
"""
Install pip in the virtual environment.
:param context: The information for the virtual environment
creation request being processed.
"""
url = 'https://raw.github.com/pypa/pip/master/contrib/get-pip.py'
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')
else:
import argparse
parser = argparse.ArgumentParser(prog=__name__,
description='Creates virtual Python '
'environments in one or '
'more target '
'directories.')
parser.add_argument('dirs', metavar='ENV_DIR', nargs='+',
help='A directory in which to create the
'virtual environment.')
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 "
"environment.")
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 os.name == 'nt':
use_symlinks = False
else:
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 '
'virtual environment '
'directory if it already '
'exists, before virtual '
'environment creation.')
parser.add_argument('--upgrade', default=False, action='store_true',
dest='upgrade', help='Upgrade the virtual '
'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,
clear=options.clear,
symlinks=options.symlinks,
upgrade=options.upgrade,
nodist=options.nodist,
nopip=options.nopip,
verbose=options.verbose)
for d in options.dirs:
builder.create(d)
if __name__ == '__main__':
rc = 1
try:
main()
rc = 0
except Exception as e:
print('Error: %s' % e, file=sys.stderr)
sys.exit(rc)
This script is also available for download online .