1:mod:`ensurepip` --- Bootstrapping the ``pip`` installer
2========================================================
3
4.. module:: ensurepip
5   :synopsis: Bootstrapping the "pip" installer into an existing Python
6              installation or virtual environment.
7
8.. versionadded:: 3.4
9
10--------------
11
12The :mod:`ensurepip` package provides support for bootstrapping the ``pip``
13installer into an existing Python installation or virtual environment. This
14bootstrapping approach reflects the fact that ``pip`` is an independent
15project with its own release cycle, and the latest available stable version
16is bundled with maintenance and feature releases of the CPython reference
17interpreter.
18
19In most cases, end users of Python shouldn't need to invoke this module
20directly (as ``pip`` should be bootstrapped by default), but it may be
21needed if installing ``pip`` was skipped when installing Python (or
22when creating a virtual environment) or after explicitly uninstalling
23``pip``.
24
25.. note::
26
27   This module *does not* access the internet. All of the components
28   needed to bootstrap ``pip`` are included as internal parts of the
29   package.
30
31.. seealso::
32
33   :ref:`installing-index`
34      The end user guide for installing Python packages
35
36   :pep:`453`: Explicit bootstrapping of pip in Python installations
37      The original rationale and specification for this module.
38
39
40Command line interface
41----------------------
42
43The command line interface is invoked using the interpreter's ``-m`` switch.
44
45The simplest possible invocation is::
46
47    python -m ensurepip
48
49This invocation will install ``pip`` if it is not already installed,
50but otherwise does nothing. To ensure the installed version of ``pip``
51is at least as recent as the one bundled with ``ensurepip``, pass the
52``--upgrade`` option::
53
54    python -m ensurepip --upgrade
55
56By default, ``pip`` is installed into the current virtual environment
57(if one is active) or into the system site packages (if there is no
58active virtual environment). The installation location can be controlled
59through two additional command line options:
60
61* ``--root <dir>``: Installs ``pip`` relative to the given root directory
62  rather than the root of the currently active virtual environment (if any)
63  or the default root for the current Python installation.
64* ``--user``: Installs ``pip`` into the user site packages directory rather
65  than globally for the current Python installation (this option is not
66  permitted inside an active virtual environment).
67
68By default, the scripts ``pipX`` and ``pipX.Y`` will be installed (where
69X.Y stands for the version of Python used to invoke ``ensurepip``). The
70scripts installed can be controlled through two additional command line
71options:
72
73* ``--altinstall``: if an alternate installation is requested, the ``pipX``
74  script will *not* be installed.
75
76* ``--default-pip``: if a "default pip" installation is requested, the
77  ``pip`` script will be installed in addition to the two regular scripts.
78
79Providing both of the script selection options will trigger an exception.
80
81
82Module API
83----------
84
85:mod:`ensurepip` exposes two functions for programmatic use:
86
87.. function:: version()
88
89   Returns a string specifying the bundled version of pip that will be
90   installed when bootstrapping an environment.
91
92.. function:: bootstrap(root=None, upgrade=False, user=False, \
93                        altinstall=False, default_pip=False, \
94                        verbosity=0)
95
96   Bootstraps ``pip`` into the current or designated environment.
97
98   *root* specifies an alternative root directory to install relative to.
99   If *root* is ``None``, then installation uses the default install location
100   for the current environment.
101
102   *upgrade* indicates whether or not to upgrade an existing installation
103   of an earlier version of ``pip`` to the bundled version.
104
105   *user* indicates whether to use the user scheme rather than installing
106   globally.
107
108   By default, the scripts ``pipX`` and ``pipX.Y`` will be installed (where
109   X.Y stands for the current version of Python).
110
111   If *altinstall* is set, then ``pipX`` will *not* be installed.
112
113   If *default_pip* is set, then ``pip`` will be installed in addition to
114   the two regular scripts.
115
116   Setting both *altinstall* and *default_pip* will trigger
117   :exc:`ValueError`.
118
119   *verbosity* controls the level of output to :data:`sys.stdout` from the
120   bootstrapping operation.
121
122   .. audit-event:: ensurepip.bootstrap root ensurepip.bootstrap
123
124   .. note::
125
126      The bootstrapping process has side effects on both ``sys.path`` and
127      ``os.environ``. Invoking the command line interface in a subprocess
128      instead allows these side effects to be avoided.
129
130   .. note::
131
132      The bootstrapping process may install additional modules required by
133      ``pip``, but other software should not assume those dependencies will
134      always be present by default (as the dependencies may be removed in a
135      future version of ``pip``).
136