Issue #15283: Updated pyvenv documentation to expand on activation.

1 files changed, 57 insertions, 3 deletions

diff --git a/Doc/library/venv.rst b/Doc/library/venv.rst
index e5c91e4620..ac0115b863 100644
--- a/Doc/library/venv.rst
+++ b/Doc/library/venv.rst
@@ -50,7 +50,7 @@ or equivalently::
 
 The command, if run with ``-h``, will show the available options::
 
-    usage: pyvenv [-h] [--system-site-packages] [--symlink] [--clear]
+    usage: pyvenv [-h] [--system-site-packages] [--symlinks] [--clear]
                   [--upgrade] ENV_DIR [ENV_DIR ...]
 
     Creates virtual Python environments in one or more target directories.
@@ -62,7 +62,8 @@ The command, if run with ``-h``, will show the available options::
       -h, --help             show this help message and exit
       --system-site-packages Give access to the global site-packages dir to the
                              virtual environment.
-      --symlink              Attempt to symlink rather than copy.
+      --symlinks             Try to use symlinks rather than copies, when symlinks
+                             are not the default for the platform.
       --clear                Delete the environment directory if it already exists.
                              If not specified and the directory exists, an error is
                              raised.
@@ -79,6 +80,56 @@ the ``--system-site-packages`` option, ``false`` otherwise.
 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: on
+a Posix platform, you would typically do::
+
+    $ source <venv>/bin/activate
+
+whereas on Windows, you might do::
+
+    c:\> <venv>/Scripts/activate
+
+if you are using the ``cmd.exe`` shell, or perhaps::
+
+    PS C:\> <venv>/Scripts/Activate.ps1
+
+if you use PowerShell.
+
+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.
+
+.. note:: A virtual environment (also called a ``venv``) 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 venv is a directory tree which contains Python executable files and
+   other files which indicate that it is a venv.
+
+   Common installation tools such as ``distribute`` and ``pip`` work as
+   expected with venvs - i.e. when a venv is active, they install Python
+   packages into the venv without needing to be told to do so explicitly.
+
+   When a venv is active (i.e. the venv's Python interpreter is running), the
+   attributes :attr:`sys.prefix` and :attr:`sys.exec_prefix` point to the base
+   directory of the venv, whereas :attr:`sys.base_prefix` and
+   :attr:`sys.base_exec_prefix` point to the non-venv Python installation
+   which was used to create the venv. If a venv is not active, then
+   :attr:`sys.prefix` is the same as :attr:`sys.base_prefix` and
+   :attr:`sys.exec_prefix` is the same as :attr:`sys.base_exec_prefix` (they
+   all point to a non-venv Python installation).
+
 
 API
 ---
@@ -105,7 +156,10 @@ creation according to their needs, the :class:`EnvBuilder` class.
       e.g. ``pythonw.exe``), rather than copying. Defaults to ``True`` on Linux and
       Unix systems, but ``False`` on Windows and Mac OS X.
 
-    .. XXX it also takes "upgrade"!
+    * ``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``).
+
 
 
     Creators of third-party virtual environment tools will be free to use the