Installing Packages

This section covers the basics of how to install Python packages.

It’s important to note that the term “package” in this context is being used as a synonym for a distribution (i.e. a bundle of software to be installed), not to refer to the kind of package that you import in your Python source code (i.e. a container of modules). It is common in the Python community to refer to a distribution using the term “package”. Using the term “distribution” is often not preferred, because it can easily be confused with a Linux distribution, or another larger software distribution like Python itself.

Requirements for Installing Packages

This section describes the steps to follow before installing other Python packages.

Ensure you can run Python from the command line

Before you go any further, make sure you have Python and that the expected version is available from your command line. You can check this by running:

python --version

You should get some output like Python 3.6.3. If you do not have Python, please install the latest 3.x version from python.org or refer to the Installing Python section of the Hitchhiker’s Guide to Python.

Note

If you’re a newcomer and you get an error like this:

>>> python --version
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'python' is not defined

It’s because this command and other suggested commands in this tutorial are intended to be run in a shell (also called a terminal or console). See the Python for Beginners getting started tutorial for an introduction to using your operating system’s shell and interacting with Python.

Note

If you’re using an enhanced shell like IPython or the Jupyter notebook, you can run system commands like those in this tutorial by prefacing them with a ! character:

In [1]: import sys
        !{sys.executable} --version
Python 3.6.3

It’s recommended to write {sys.executable} rather than plain python in order to ensure that commands are run in the Python installation matching the currently running notebook (which may not be the same Python installation that the python command refers to).

Note

Due to the way most Linux distributions are handling the Python 3 migration, Linux users using the system Python without creating a virtual environment first should replace the python command in this tutorial with python3 and the pip command with pip3 --user. Do not run any of the commands in this tutorial with sudo: if you get a permissions error, come back to the section on creating virtual environments, set one up, and then continue with the tutorial as written.

Ensure you can run pip from the command line

Additionally, you’ll need to make sure you have pip available. You can check this by running:

pip --version

If you installed Python from source, with an installer from python.org, or via Homebrew you should already have pip. If you’re on Linux and installed using your OS package manager, you may have to install pip separately, see Installing pip/setuptools/wheel with Linux Package Managers.

If pip isn’t already installed, then first try to bootstrap it from the standard library:

python -m ensurepip --default-pip

If that still doesn’t allow you to run pip:

  • Securely Download get-pip.py [1]

  • Run python get-pip.py. [2] This will install or upgrade pip. Additionally, it will install setuptools and wheel if they’re not installed already.

    Warning

    Be cautious if you’re using a Python install that’s managed by your operating system or another package manager. get-pip.py does not coordinate with those tools, and may leave your system in an inconsistent state. You can use python get-pip.py --prefix=/usr/local/ to install in /usr/local which is designed for locally-installed software.

Ensure pip, setuptools, and wheel are up to date

While pip alone is sufficient to install from pre-built binary archives, up to date copies of the setuptools and wheel projects are useful to ensure you can also install from source archives:

python -m pip install --upgrade pip setuptools wheel

Optionally, create a virtual environment

See section below for details, but here’s the basic venv [3] command to use on a typical Linux system:

python3 -m venv tutorial_env
source tutorial_env/bin/activate

This will create a new virtual environment in the tutorial_env subdirectory, and configure the current shell to use it as the default python environment.

Creating Virtual Environments

Python “Virtual Environments” allow Python packages to be installed in an isolated location for a particular application, rather than being installed globally.

Imagine you have an application that needs version 1 of LibFoo, but another application requires version 2. How can you use both these applications? If you install everything into /usr/lib/python3.6/site-packages (or whatever your platform’s standard location is), it’s easy to end up in a situation where you unintentionally upgrade an application that shouldn’t be upgraded.

Or more generally, what if you want to install an application and leave it be? If an application works, any change in its libraries or the versions of those libraries can break the application.

Also, what if you can’t install packages into the global site-packages directory? For instance, on a shared host.

In all these cases, virtual environments can help you. They have their own installation directories and they don’t share libraries with other virtual environments.

Currently, there are two common tools for creating Python virtual environments:

  • venv is available by default in Python 3.3 and later, and installs pip and setuptools into created virtual environments in Python 3.4 and later.
  • virtualenv needs to be installed separately, but supports Python 2.6+ and Python 3.3+, and pip, setuptools and wheel are always installed into created virtual environments by default (regardless of Python version).

The basic usage is like so:

Using virtualenv:

virtualenv <DIR>
source <DIR>/bin/activate

Using venv:

python3 -m venv <DIR>
source <DIR>/bin/activate

For more information, see the virtualenv docs or the venv docs.

In both of the above cases, Windows users should _not_ use the source command, but should rather run the activate script directly from the command shell. The use of source under Unix shells ensures that the virtual environment’s variables are set within the current shell, and not in a subprocess (which then disappears, having no useful effect).

Managing multiple virtual environments directly can become tedious, so the dependency management tutorial introduces a higher level tool, Pipenv, that automatically manages a separate virtual environment for each project and application that you work on.

Use pip for Installing

pip is the recommended installer. Below, we’ll cover the most common usage scenarios. For more detail, see the pip docs, which includes a complete Reference Guide.

Installing from PyPI

The most common usage of pip is to install from the Python Package Index using a requirement specifier. Generally speaking, a requirement specifier is composed of a project name followed by an optional version specifier. PEP 440 contains a full specification of the currently supported specifiers. Below are some examples.

To install the latest version of “SomeProject”:

pip install 'SomeProject'

To install a specific version:

pip install 'SomeProject==1.4'

To install greater than or equal to one version and less than another:

pip install 'SomeProject>=1,<2'

To install a version that’s “compatible” with a certain version: [4]

pip install 'SomeProject~=1.4.2'

In this case, this means to install any version “==1.4.*” version that’s also “>=1.4.2”.

Source Distributions vs Wheels

pip can install from either Source Distributions (sdist) or Wheels, but if both are present on PyPI, pip will prefer a compatible wheel.

Wheels are a pre-built distribution format that provides faster installation compared to Source Distributions (sdist), especially when a project contains compiled extensions.

If pip does not find a wheel to install, it will locally build a wheel and cache it for future installs, instead of rebuilding the source distribution in the future.

Upgrading packages

Upgrade an already installed SomeProject to the latest from PyPI.

pip install --upgrade SomeProject

Installing to the User Site

To install packages that are isolated to the current user, use the --user flag:

pip install --user SomeProject

For more information see the User Installs section from the pip docs.

Note that the --user flag has no effect when inside a virtual environment - all installation commands will affect the virtual environment.

Requirements files

Install a list of requirements specified in a Requirements File.

pip install -r requirements.txt

Installing from VCS

Install a project from VCS in “editable” mode. For a full breakdown of the syntax, see pip’s section on VCS Support.

pip install -e git+https://git.repo/some_pkg.git#egg=SomeProject          # from git
pip install -e hg+https://hg.repo/some_pkg#egg=SomeProject                # from mercurial
pip install -e svn+svn://svn.repo/some_pkg/trunk/#egg=SomeProject         # from svn
pip install -e git+https://git.repo/some_pkg.git@feature#egg=SomeProject  # from a branch

Installing from other Indexes

Install from an alternate index

pip install --index-url http://my.package.repo/simple/ SomeProject

Search an additional index during install, in addition to PyPI

pip install --extra-index-url http://my.package.repo/simple SomeProject

Installing from a local src tree

Installing from local src in Development Mode, i.e. in such a way that the project appears to be installed, but yet is still editable from the src tree.

pip install -e <path>

You can also install normally from src

pip install <path>

Installing from local archives

Install a particular source archive file.

pip install ./downloads/SomeProject-1.0.4.tar.gz

Install from a local directory containing archives (and don’t check PyPI)

pip install --no-index --find-links=file:///local/dir/ SomeProject
pip install --no-index --find-links=/local/dir/ SomeProject
pip install --no-index --find-links=relative/dir/ SomeProject

Installing from other sources

To install from other data sources (for example Amazon S3 storage) you can create a helper application that presents the data in a PEP 503 compliant index format, and use the --extra-index-url flag to direct pip to use that index.

./s3helper --port=7777
pip install --extra-index-url http://localhost:7777 SomeProject

Installing Prereleases

Find pre-release and development versions, in addition to stable versions. By default, pip only finds stable versions.

pip install --pre SomeProject

Installing Setuptools “Extras”

Install setuptools extras.

$ pip install SomePackage[PDF]
$ pip install SomePackage[PDF]==3.0
$ pip install -e .[PDF]==3.0  # editable project in current directory

[1]“Secure” in this context means using a modern browser or a tool like curl that verifies SSL certificates when downloading from https URLs.
[2]Depending on your platform, this may require root or Administrator access. pip is currently considering changing this by making user installs the default behavior.
[3]Beginning with Python 3.4, venv (a stdlib alternative to virtualenv) will create virtualenv environments with pip pre-installed, thereby making it an equal alternative to virtualenv.
[4]The compatible release specifier was accepted in PEP 440 and support was released in setuptools v8.0 and pip v6.0