28.3. venv — 仮想環境の作成

バージョン 3.3 で追加.

ソースコード: Lib/venv/

venv モジュールは、軽量な “仮想環境” の作成のサポートを提供します。仮想環境には、仮想環境ごとの site ディレクトリがあり、これはシステムの site ディレクトリから分離させることができます。それぞれの仮想環境には、それ自身の Python バイナリ (様々な Python バージョンで環境を作成できます) があり、仮想環境ごとの site ディレクトリに独立した Python パッケージ群をインストールできます。

Python仮想環境に関してより詳しくは PEP 405 を参照してください。


The 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.

28.3.1. 仮想環境の作成

Creation of virtual environments 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 (or Scripts on Windows) subdirectory containing a copy of the python binary (or binaries, in the case of Windows). It also creates an (initially empty) lib/pythonX.Y/site-packages subdirectory (on Windows, this is Lib\site-packages).

バージョン 3.6 で撤廃: pyvenv was the recommended tool for creating virtual environments for Python 3.3 and 3.4, and is deprecated in Python 3.6.

バージョン 3.5 で変更: 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 myenv c:\path\to\myenv

このコマンドを -h をつけて実行すると利用できるオプションが表示されます:

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
                        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.

バージョン 3.4 で変更: デフォルトで pip をインストールします。--without-pip--copies オプションを追加しました。

バージョン 3.4 で変更: 以前のバージョンでは --clear--upgrade オプションが指定されていない限り、対象のディレクトリが既に存在していた場合はエラーを送出していました。 現在は、既存のディレクトリが指定された場合、中身が削除されディレクトリは新規作成されたように扱われます。

作成された pyvenv.cfg ファイルには、include-system-site-packages キーも含まれます。これは venv--system-site-packages オプションをつけて実行されたなら true で、そうでなければ false です。

--without-pip オプションが与えられない限り、pip を仮想環境でブートするために ensurepip が呼ばれます。

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:




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.

バージョン 3.4 で追加: fish および csh 有効化スクリプト。


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 is the same as sys.base_prefix and sys.exec_prefix is the same as 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.

28.3.2. API

上述の高水準のメソッドは、サードパーティの仮想環境クリエータが環境の作成を必要に応じてカスタマイズするための機構を提供する簡素な API を利用します。それが EnvBuilder クラスです。

class venv.EnvBuilder(system_site_packages=False, clear=False, symlinks=False, upgrade=False, with_pip=False, prompt=None)

EnvBuilder クラスを実体化するときに、以下のキーワード引数を受け取ります:

  • system_site_packages – 真偽値で、システムの Python の site-packages を仮想環境から利用できるかどうかを示します (デフォルト: False)。

  • clear – 真偽値で、真の場合環境を作成する前に既存の対象ディレクトリの中身を削除します。

  • symlinks – 真偽値で、Python のバイナリ (と必要な DLL や pythonw.exe などのバイナリ) をコピーせずにシンボリックの作成を試みるかどうかを示します。デフォルトは Linux や Unix システムでは True ですが、Windows では False です。

  • upgrade – 真偽値で、真の場合実行中の Python で既存の環境をアップグレードします。その Python がインプレースでアップグレードされたときに用います。デフォルトは False です。

  • with_pip – 真偽値で、真の場合仮想環境に pip がインストールされていることを保証します。--default-pip オプションで ensurepip を使用します。

  • prompt – a String to be used after virtual environment is activated (defaults to None which means directory name of the environment would be used).

バージョン 3.4 で変更: with_pip 引数が追加されました。

バージョン 3.6 で追加: Added the prompt parameter

サードパーティーの仮想環境ツールのクリエータは、EnvBuilder を継承して使うことができます。

返される env-builder オブジェクトには create というメソッドがあります:


このメソッドは path (絶対パスあるいは現在のディレクトリからの相対パス) を必要な1つの引数と受け取ります。create メソッドは指定されたディレクトリに仮想環境を構築するか、例外を送出します。

EnvBuilder クラスの create メソッドは、サブクラスのカスタマイズに使えるフックを説明します:

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)

Each of the methods ensure_directories(), create_configuration(), setup_python(), setup_scripts() and post_setup() can be overridden.


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.


仮想環境に pyvenv.cfg 設定ファイルを作成します。


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.





これらに加えて、 EnvBuildersetup_scripts() やサブクラスの post_setup() が仮想環境にスクリプトをインストールするためのユーティリティーメソッドを提供しています。

install_scripts(context, path)

path は “common”, “posix”, “nt” ディレクトリを格納したディレクトリへのパスです。各サブディレクトリには仮想環境の bin ディレクトリにインストールするスクリプトを格納します。 “common” の中身と、 os.name に一致するディレクトリの中身を、以下の置換処理を行いながらコピーします:

  • __VENV_DIR__ は仮想環境ディレクトリの絶対パスに置換されます。

  • __VENV_NAME__ は仮想環境の名前 (仮想環境ディレクトリのパスの最後の部分) に置換されます。

  • __VENV_PROMPT__ はプロンプトに置換されます (括弧で囲まれ空白が続く環境名)。

  • __VENV_BIN_NAME__ は bin ディレクトリ名 (binScripts) に置換されます。

  • __VENV_PYTHON__ は仮想環境の Python 実行ファイルの絶対パスに置換されます。

(既存環境のアップグレード中は) ディレクトリは存在しても構いません。


venv.create(env_dir, system_site_packages=False, clear=False, symlinks=False, with_pip=False)

EnvBuilder を指定されたキーワード引数を使って作成し、その create() メソッドに env_dir 引数を渡して実行します。

バージョン 3.4 で変更: with_pip 引数が追加されました。

28.3.3. EnvBuilder を拡張する例

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:
        # 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 virtual environment'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 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'))
        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 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)

    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')
        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 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 "
        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
            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 '
        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)

このスクリプトは オンライン でダウンロードすることも可能です。