1 2 .. _tut-venv: 3 4 ********************************* 5 Virtual Environments and Packages 6 ********************************* 7 8 Introduction 9 ============ 10 11 Python applications will often use packages and modules that don't 12 come as part of the standard library. Applications will sometimes 13 need a specific version of a library, because the application may 14 require that a particular bug has been fixed or the application may be 15 written using an obsolete version of the library's interface. 16 17 This means it may not be possible for one Python installation to meet 18 the requirements of every application. If application A needs version 19 1.0 of a particular module but application B needs version 2.0, then 20 the requirements are in conflict and installing either version 1.0 or 2.0 21 will leave one application unable to run. 22 23 The solution for this problem is to create a :term:`virtual environment`, a 24 self-contained directory tree that contains a Python installation for a 25 particular version of Python, plus a number of additional packages. 26 27 Different applications can then use different virtual environments. 28 To resolve the earlier example of conflicting requirements, 29 application A can have its own virtual environment with version 1.0 30 installed while application B has another virtual environment with version 2.0. 31 If application B requires a library be upgraded to version 3.0, this will 32 not affect application A's environment. 33 34 35 Creating Virtual Environments 36 ============================= 37 38 The module used to create and manage virtual environments is called 39 :mod:`venv`. :mod:`venv` will usually install the most recent version of 40 Python that you have available. If you have multiple versions of Python on your 41 system, you can select a specific Python version by running ``python3`` or 42 whichever version you want. 43 44 To create a virtual environment, decide upon a directory where you want to 45 place it, and run the :mod:`venv` module as a script with the directory path:: 46 47 python3 -m venv tutorial-env 48 49 This will create the ``tutorial-env`` directory if it doesn't exist, 50 and also create directories inside it containing a copy of the Python 51 interpreter, the standard library, and various supporting files. 52 53 Once you've created a virtual environment, you may activate it. 54 55 On Windows, run:: 56 57 tutorial-env\Scripts\activate.bat 58 59 On Unix or MacOS, run:: 60 61 source tutorial-env/bin/activate 62 63 (This script is written for the bash shell. If you use the 64 :program:`csh` or :program:`fish` shells, there are alternate 65 ``activate.csh`` and ``activate.fish`` scripts you should use 66 instead.) 67 68 Activating the virtual environment will change your shell's prompt to show what 69 virtual environment you're using, and modify the environment so that running 70 ``python`` will get you that particular version and installation of Python. 71 For example: 72 73 .. code-block:: bash 74 75 $ source ~/envs/tutorial-env/bin/activate 76 (tutorial-env) $ python 77 Python 3.5.1 (default, May 6 2016, 10:59:36) 78 ... 79 >>> import sys 80 >>> sys.path 81 ['', '/usr/local/lib/python35.zip', ..., 82 '~/envs/tutorial-env/lib/python3.5/site-packages'] 83 >>> 84 85 86 Managing Packages with pip 87 ========================== 88 89 You can install, upgrade, and remove packages using a program called 90 :program:`pip`. By default ``pip`` will install packages from the Python 91 Package Index, <https://pypi.python.org/pypi>. You can browse the Python 92 Package Index by going to it in your web browser, or you can use ``pip``'s 93 limited search feature: 94 95 .. code-block:: bash 96 97 (tutorial-env) $ pip search astronomy 98 skyfield - Elegant astronomy for Python 99 gary - Galactic astronomy and gravitational dynamics. 100 novas - The United States Naval Observatory NOVAS astronomy library 101 astroobs - Provides astronomy ephemeris to plan telescope observations 102 PyAstronomy - A collection of astronomy related tools for Python. 103 ... 104 105 ``pip`` has a number of subcommands: "search", "install", "uninstall", 106 "freeze", etc. (Consult the :ref:`installing-index` guide for 107 complete documentation for ``pip``.) 108 109 You can install the latest version of a package by specifying a package's name: 110 111 .. code-block:: bash 112 113 (tutorial-env) $ pip install novas 114 Collecting novas 115 Downloading novas-3.1.1.3.tar.gz (136kB) 116 Installing collected packages: novas 117 Running setup.py install for novas 118 Successfully installed novas-3.1.1.3 119 120 You can also install a specific version of a package by giving the 121 package name followed by ``==`` and the version number: 122 123 .. code-block:: bash 124 125 (tutorial-env) $ pip install requests==2.6.0 126 Collecting requests==2.6.0 127 Using cached requests-2.6.0-py2.py3-none-any.whl 128 Installing collected packages: requests 129 Successfully installed requests-2.6.0 130 131 If you re-run this command, ``pip`` will notice that the requested 132 version is already installed and do nothing. You can supply a 133 different version number to get that version, or you can run ``pip 134 install --upgrade`` to upgrade the package to the latest version: 135 136 .. code-block:: bash 137 138 (tutorial-env) $ pip install --upgrade requests 139 Collecting requests 140 Installing collected packages: requests 141 Found existing installation: requests 2.6.0 142 Uninstalling requests-2.6.0: 143 Successfully uninstalled requests-2.6.0 144 Successfully installed requests-2.7.0 145 146 ``pip uninstall`` followed by one or more package names will remove the 147 packages from the virtual environment. 148 149 ``pip show`` will display information about a particular package: 150 151 .. code-block:: bash 152 153 (tutorial-env) $ pip show requests 154 --- 155 Metadata-Version: 2.0 156 Name: requests 157 Version: 2.7.0 158 Summary: Python HTTP for Humans. 159 Home-page: http://python-requests.org 160 Author: Kenneth Reitz 161 Author-email: me (a] kennethreitz.com 162 License: Apache 2.0 163 Location: /Users/akuchling/envs/tutorial-env/lib/python3.4/site-packages 164 Requires: 165 166 ``pip list`` will display all of the packages installed in the virtual 167 environment: 168 169 .. code-block:: bash 170 171 (tutorial-env) $ pip list 172 novas (3.1.1.3) 173 numpy (1.9.2) 174 pip (7.0.3) 175 requests (2.7.0) 176 setuptools (16.0) 177 178 ``pip freeze`` will produce a similar list of the installed packages, 179 but the output uses the format that ``pip install`` expects. 180 A common convention is to put this list in a ``requirements.txt`` file: 181 182 .. code-block:: bash 183 184 (tutorial-env) $ pip freeze > requirements.txt 185 (tutorial-env) $ cat requirements.txt 186 novas==3.1.1.3 187 numpy==1.9.2 188 requests==2.7.0 189 190 The ``requirements.txt`` can then be committed to version control and 191 shipped as part of an application. Users can then install all the 192 necessary packages with ``install -r``: 193 194 .. code-block:: bash 195 196 (tutorial-env) $ pip install -r requirements.txt 197 Collecting novas==3.1.1.3 (from -r requirements.txt (line 1)) 198 ... 199 Collecting numpy==1.9.2 (from -r requirements.txt (line 2)) 200 ... 201 Collecting requests==2.7.0 (from -r requirements.txt (line 3)) 202 ... 203 Installing collected packages: novas, numpy, requests 204 Running setup.py install for novas 205 Successfully installed novas-3.1.1.3 numpy-1.9.2 requests-2.7.0 206 207 ``pip`` has many more options. Consult the :ref:`installing-index` 208 guide for complete documentation for ``pip``. When you've written 209 a package and want to make it available on the Python Package Index, 210 consult the :ref:`distributing-index` guide. 211
