Implement PEP 477 - Backport ensurepip (PEP 453) to 2.7

* Backports ensurepip to the 2.7 branch
* Backports some of the improved documentation to the 2.7 branch.
* Adds a private backport of the 3.x mock library as test._mock_backport
  to enable saner testing of ensurepip.

Key Differences from 3.x:

* Ensurepip does not have any Makefile integration, specifically
  it is not ran by default in the Makefile.
* There is no venv module in 2.7, so downstream distributors can
  completely disable ensurepip, ideally with a message redirecting
  to the correct way to install pip.
* To match the ``python`` command in 2.7, ensurepip will install
  the unversioned ``pip`` command as well.
* No-op and hide --default-pip and add --no-default-pip to restore
  the 3.x behavor on 2.7.

5 files changed, 203 insertions, 1 deletions

diff --git a/Doc/library/distribution.rst b/Doc/library/distribution.rst
new file mode 100644
index 0000000..b560999
--- /dev/null
+++ b/Doc/library/distribution.rst
@@ -0,0 +1,13 @@
+***********************************
+Software Packaging and Distribution
+***********************************
+
+These libraries help you with publishing and installing Python software.
+While these modules are designed to work in conjunction with the
+`Python Package Index <https://pypi.python.org>`__, they can also be used
+with a local index server, or without any index server at all.
+
+.. toctree::
+
+   distutils.rst
+   ensurepip.rst
diff --git a/Doc/library/ensurepip.rst b/Doc/library/ensurepip.rst
new file mode 100644
index 0000000..7206300
--- /dev/null
+++ b/Doc/library/ensurepip.rst
@@ -0,0 +1,130 @@
+:mod:`ensurepip` --- Bootstrapping the ``pip`` installer
+========================================================
+
+.. module:: ensurepip
+   :synopsis: Bootstrapping the ``pip`` installer into an existing Python
+              installation or virtual environment.
+
+.. versionadded:: 2.7.9
+
+The :mod:`ensurepip` package provides support for bootstrapping the ``pip``
+installer into an existing Python installation or virtual environment. This
+bootstrapping approach reflects the fact that ``pip`` is an independent
+project with its own release cycle, and the latest available stable version
+is bundled with maintenance and feature releases of the CPython reference
+interpreter.
+
+In most cases, end users of Python shouldn't need to invoke this module
+directly (as ``pip`` should be bootstrapped by default), but it may be
+needed if installing ``pip`` was skipped when installing Python (or
+when creating a virtual environment) or after explicitly uninstalling ``pip``.
+
+.. note::
+
+   This module *does not* access the internet. All of the components
+   needed to bootstrap ``pip`` are included as internal parts of the
+   package.
+
+.. seealso::
+
+   :ref:`installing-index`
+      The end user guide for installing Python packages
+
+   :pep:`453`: Explicit bootstrapping of pip in Python installations
+      The original rationale and specification for this module.
+
+   :pep:`477`: Backport ensurepip (PEP 453) to Python 2.7
+      The rationale and specification for backporting PEP 453 to Python 2.7.
+
+
+Command line interface
+----------------------
+
+The command line interface is invoked using the interpreter's ``-m`` switch.
+
+The simplest possible invocation is::
+
+    python -m ensurepip
+
+This invocation will install ``pip`` if it is not already installed,
+but otherwise does nothing. To ensure the installed version of ``pip``
+is at least as recent as the one bundled with ``ensurepip``, pass the
+``--upgrade`` option::
+
+    python -m ensurepip --upgrade
+
+By default, ``pip`` is installed into the current virtual environment
+(if one is active) or into the system site packages (if there is no
+active virtual environment). The installation location can be controlled
+through two additional command line options:
+
+* ``--root <dir>``: Installs ``pip`` relative to the given root directory
+  rather than the root of the currently active virtual environment (if any)
+  or the default root for the current Python installation.
+* ``--user``: Installs ``pip`` into the user site packages directory rather
+  than globally for the current Python installation (this option is not
+  permitted inside an active virtual environment).
+
+By default, the scripts ``pip``, ``pipX``, and ``pipX.Y`` will be installed
+(where X.Y stands for the version of Python used to invoke ``ensurepip``). The
+scripts installed can be controlled through two additional command line
+options:
+
+* ``--altinstall``: if an alternate installation is requested, the ``pip`` and
+  ``pipX`` script will *not* be installed.
+
+* ``--no-default-pip``: if a non-default installation is request, the ``pip``
+  script will *not* be installed.
+
+
+Module API
+----------
+
+:mod:`ensurepip` exposes two functions for programmatic use:
+
+.. function:: version()
+
+   Returns a string specifying the bundled version of pip that will be
+   installed when bootstrapping an environment.
+
+.. function:: bootstrap(root=None, upgrade=False, user=False, \
+                        altinstall=False, default_pip=True, \
+                        verbosity=0)
+
+   Bootstraps ``pip`` into the current or designated environment.
+
+   *root* specifies an alternative root directory to install relative to.
+   If *root* is None, then installation uses the default install location
+   for the current environment.
+
+   *upgrade* indicates whether or not to upgrade an existing installation
+   of an earlier version of ``pip`` to the bundled version.
+
+   *user* indicates whether to use the user scheme rather than installing
+   globally.
+
+   By default, the scripts ``pip``, ``pipX``, and ``pipX.Y`` will be installed
+   (where X.Y stands for the current version of Python).
+
+   If *altinstall* is set, then ``pip`` and ``pipX`` will *not* be installed.
+
+   If *default_pip* is set to ``False``, then ``pip`` will *not* be installed.
+
+   Setting both *altinstall* and *default_pip* will trigger
+   :exc:`ValueError`.
+
+   *verbosity* controls the level of output to :data:`sys.stdout` from the
+   bootstrapping operation.
+
+   .. note::
+
+      The bootstrapping process has side effects on both ``sys.path`` and
+      ``os.environ``. Invoking the command line interface in a subprocess
+      instead allows these side effects to be avoided.
+
+   .. note::
+
+      The bootstrapping process may install additional modules required by
+      ``pip``, but other software should not assume those dependencies will
+      always be present by default (as the dependencies may be removed in a
+      future version of ``pip``).
diff --git a/Doc/library/index.rst b/Doc/library/index.rst
index 5d335e4..4b465d9 100644
--- a/Doc/library/index.rst
+++ b/Doc/library/index.rst
@@ -63,6 +63,7 @@ the `Python Package Index <https://pypi.python.org/pypi>`_.
    tk.rst
    development.rst
    debug.rst
+   distribution.rst
    python.rst
    custominterp.rst
    restricted.rst
diff --git a/Doc/library/python.rst b/Doc/library/python.rst
index aaf1abd..1ebc329 100644
--- a/Doc/library/python.rst
+++ b/Doc/library/python.rst
@@ -28,4 +28,3 @@ overview:
    site.rst
    user.rst
    fpectl.rst
-   distutils.rst
diff --git a/Doc/whatsnew/2.7.rst b/Doc/whatsnew/2.7.rst
index 9d26893..3fde2d8 100644
--- a/Doc/whatsnew/2.7.rst
+++ b/Doc/whatsnew/2.7.rst
@@ -2575,6 +2575,65 @@ with the first of those changes appearing in the Python 2.7.7 release.
   Gaynor; :issue:`21305`.)
 
 
+PEP 477: Backport ensurepip (PEP 453) to Python 2.7
+---------------------------------------------------
+
+:pep:`477` approves the inclusion of the :pep:`453` ensurepip module and the
+improved documentation that was enabled by it in the Python 2.7 maintenance
+releases, appearing first in the the Python 2.7.9 release.
+
+
+Bootstrapping pip By Default
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The new :mod:`ensurepip` module (defined in :pep:`453`) provides a standard
+cross-platform mechanism to bootstrap the pip installer into Python
+installations. The version of ``pip`` included with Python 2.7.9 is ``pip``
+1.5.6, and future 2.7.x maintenance releases will update the bundled version to
+the latest version of ``pip`` that is available at the time of creating the
+release candidate.
+
+By default, the commands ``pip``, ``pipX`` and ``pipX.Y`` will be installed on
+all platforms (where X.Y stands for the version of the Python installation),
+along with the ``pip`` Python package and its dependencies.
+
+On Windows and Mac OS X, the CPython installers now default to installing
+``pip`` along with CPython itself (users may opt out of installing it
+during the installation process). Window users will need to opt in to the
+automatic ``PATH`` modifications to have ``pip`` available from the command
+line by default, otherwise it can still be accessed through the Python
+launcher for Windows as ``py -m pip``.
+
+As `discussed in the PEP`__, platform packagers may choose not to install
+these commands by default, as long as, when invoked, they provide clear and
+simple directions on how to install them on that platform (usually using
+the system package manager).
+
+__ https://www.python.org/dev/peps/pep-0477/#disabling-ensurepip-by-downstream-distributors
+
+
+Documentation Changes
+~~~~~~~~~~~~~~~~~~~~~
+
+As part of this change, the :ref:`installing-index` and
+:ref:`distributing-index` sections of the documentation have been
+completely redesigned as short getting started and FAQ documents. Most
+packaging documentation has now been moved out to the Python Packaging
+Authority maintained `Python Packaging User Guide
+<http://packaging.python.org>`__ and the documentation of the individual
+projects.
+
+However, as this migration is currently still incomplete, the legacy
+versions of those guides remaining available as :ref:`install-index`
+and :ref:`distutils-index`.
+
+.. seealso::
+
+   :pep:`453` -- Explicit bootstrapping of pip in Python installations
+      PEP written by Donald Stufft and Nick Coghlan, implemented by
+      Donald Stufft, Nick Coghlan, Martin von Löwis and Ned Deily.
+
+
 .. ======================================================================
 
 .. _acks27: