5. Additional Tools and Scripts - Python 3.5.9 documentation 编辑
5.1. pyvenv - Creating virtual environments
Creation of virtual environments is done by executing the pyvenv
script:
pyvenv /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 the command was run from. 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
).
See also
Python Packaging User Guide: Creating and using virtual environments
On Windows, you may have to invoke the pyvenv
script as follows, if you don’t have the relevant PATH and PATHEXT settings:
c:\Temp>c:\Python35\python c:\Python35\Tools\Scripts\pyvenv.py myenv
or equivalently:
c:\Temp>c:\Python35\python -m venv 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)
Depending on how the venv
functionality has been invoked, the usage message may vary slightly, e.g. referencing pyvenv
rather than venv
.
Changed in version 3.4: Installs pip by default, added the --without-pip
and --copies
options
Changed in version 3.4: In earlier versions, if the target directory already existed, an error was raised, unless the --clear
or --upgrade
option was provided. Now, if an existing directory is specified, its contents are removed and the directory is processed as if it had been newly created.
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
otherwise.
Unless the --without-pip
option is given, ensurepip
will be invoked to bootstrap pip
into the virtual environment.
Multiple paths can be given to pyvenv
, in which case an identical virtualenv will be created, according to the given options, at each provided path.
Once a venv has been created, it can be “activated” using a script in the venv’s binary directory. The invocation of the script is platform-specific:
Platform | 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 venv’s binary directory to your path, so that “python” invokes the venv’s Python interpreter and you can run installed scripts without having to use their full path. However, all scripts installed in a venv should be runnable without activating it, and run with the venv’s Python automatically.
You can deactivate a venv 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 venv is created.
New in version 3.4: fish
and csh
activation scripts.
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