python-setup

Installing Python Modules

As a popular open source development project, Python has an active supporting community of contributors and users that also make their software available for other Python developers to use under open source license terms.

This allows Python users to share and collaborate effectively, benefiting from the solutions others have already created to common (and sometimes even rare!) problems, as well as potentially contributing their own solutions to the common pool.

This guide covers the installation part of the process. For a guide to creating and sharing your own Python projects, refer to the distribution guide.

Note

For corporate and other institutional users, be aware that many organisations have their own policies around using and contributing to open source software. Please take such policies into account when making use of the distribution and installation tools provided with Python.

Key terms

pip is the preferred installer program. Starting with Python 3.4, it is included by default with the Python binary installers.
A virtual environment is a semi-isolated Python environment that allows packages to be installed for use by a particular application, rather than being installed system wide.
venv is the standard tool for creating virtual environments, and has been part of Python since Python 3.3. Starting with Python 3.4, it defaults to installing pip into all created virtual environments.
virtualenv is a third party alternative (and predecessor) to venv. It allows virtual environments to be used on versions of Python prior to 3.4, which either don’t provide venv at all, or aren’t able to automatically install pip into created environments.
The Python Packaging Index is a public repository of open source licensed packages made available for use by other Python users.
the Python Packaging Authority is the group of developers and documentation authors responsible for the maintenance and evolution of the standard packaging tools and the associated metadata and file format standards. They maintain a variety of tools, documentation, and issue trackers on both GitHub and Bitbucket.
distutils is the original build and distribution system first added to the Python standard library in 1998. While direct use of distutils is being phased out, it still laid the foundation for the current packaging and distribution infrastructure, and it not only remains part of the standard library, but its name lives on in other ways (such as the name of the mailing list used to coordinate Python packaging standards development).

Changed in version 3.5: The use of venv is now recommended for creating virtual environments.

Basic usage

The standard packaging tools are all designed to be used from the command line.

The following command will install the latest version of a module and its dependencies from the Python Packaging Index:

python -m pip install SomePackage

Note

For POSIX users (including Mac OS X and Linux users), the examples in this guide assume the use of a virtual environment.

For Windows users, the examples in this guide assume that the option to adjust the system PATH environment variable was selected when installing Python.

It’s also possible to specify an exact or minimum version directly on the command line. When using comparator operators such as >, < or some other special character which get interpreted by shell, the package name and the version should be enclosed within double quotes:

python -m pip install SomePackage==1.0.4    # specific version
python -m pip install "SomePackage>=1.0.4"  # minimum version

Normally, if a suitable module is already installed, attempting to install it again will have no effect. Upgrading existing modules must be requested explicitly:

python -m pip install --upgrade SomePackage

More information and resources regarding pip and its capabilities can be found in the Python Packaging User Guide.

Creation of virtual environments is done through the venv module. Installing packages into an active virtual environment uses the commands shown above.

How do I …?

These are quick answers or links for some common tasks.

… install `pip` in versions of Python prior to Python 3.4?

Python only started bundling pip with Python 3.4. For earlier versions, pip needs to be “bootstrapped” as described in the Python Packaging User Guide.

… install packages just for the current user?

Passing the --user option to python -m pip install will install a package just for the current user, rather than for all users of the system.

… install scientific Python packages?

A number of scientific Python packages have complex binary dependencies, and aren’t currently easy to install using pip directly. At this point in time, it will often be easier for users to install these packages by other means rather than attempting to install them with pip.

… work with multiple versions of Python installed in parallel?

On Linux, Mac OS X, and other POSIX systems, use the versioned Python commands in combination with the -m switch to run the appropriate copy of pip:

python2   -m pip install SomePackage  # default Python 2
python2.7 -m pip install SomePackage  # specifically Python 2.7
python3   -m pip install SomePackage  # default Python 3
python3.4 -m pip install SomePackage  # specifically Python 3.4

Appropriately versioned pip commands may also be available.

On Windows, use the py Python launcher in combination with the -m switch:

py -2   -m pip install SomePackage  # default Python 2
py -2.7 -m pip install SomePackage  # specifically Python 2.7
py -3   -m pip install SomePackage  # default Python 3
py -3.4 -m pip install SomePackage  # specifically Python 3.4

Common installation issues

Installing into the system Python on Linux

On Linux systems, a Python installation will typically be included as part of the distribution. Installing into this Python installation requires root access to the system, and may interfere with the operation of the system package manager and other components of the system if a component is unexpectedly upgraded using pip.

On such systems, it is often better to use a virtual environment or a per-user installation when installing packages with pip.

Pip not installed

It is possible that pip does not get installed by default. One potential fix is:

python -m ensurepip --default-pip

There are also additional resources for installing pip.

Installing binary extensions

Python has typically relied heavily on source based distribution, with end users being expected to compile extension modules from source as part of the installation process.

With the introduction of support for the binary wheel format, and the ability to publish wheels for at least Windows and Mac OS X through the Python Packaging Index, this problem is expected to diminish over time, as users are more regularly able to install pre-built extensions rather than needing to build them themselves.

Some of the solutions for installing scientific software that are not yet available as pre-built wheel files may also help with obtaining other binary extensions without needing to build them locally.

Alternate Python Setup:

Python Installation Instructions

Python is the second programming language we will use in this course.

Note: We do not install the python using the installer from the python.org website in this course. If you have one installed you should uninstall it before installing this version of python.

Currently the curriculum for this course is compatible with Python 3.9.

Installing pyenv

The first thing we need is to install the Python version manager (pyenv). This is similar to the nvm tool we used to install Node.JS, except it controls what versions of python we use on our system.

To install pyenv we use the pyenv-installer

From the installation instructions on the pyenv-installer website, it says we run the following command:

curl https://pyenv.run | bash

Unlike nvm, pyenv does not automatically add it's startup lines to your shell startup file.

The files that you have to change will depend on which shell you are running (you can check which shell you have by running echo $SHELL). Follow the instructions to update the startup files associated with the shell that you are running.

If your shell is `zsh`

Open up your .profile file with the following command.

code ~/.profile

Add the following lines to your .profile.

export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"

Open up your .zprofile file with the following command.

code ~/.zprofile

Add the following lines to your .zprofile. (Yes, these are the same as above.)

export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"

Open your .zshrc with the following command

code ~/.zshrc

Add the following line.

eval "$(pyenv init -)"

If your shell is `bash`

Open up your .profile file with the following command.

code ~/.profile

Add the following lines.

export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"

Check if you have a .bash_profile. Run the following at the command line if you don't know.

if [ -f ~/.bash_profile ]; then echo "bash_profile exists"; else echo "bash_profile does not exist"; fi

If you don't have a .bash_profile, you can skip the rest of this step. If you do, open up your .bash_profile file with the following command.

code ~/.bash_profile

Add the following lines to your .bash_profile. (Yes, these are the same as above.)

export PYENV_ROOT="$HOME/.pyenv"
export PATH="$PYENV_ROOT/bin:$PATH"
eval "$(pyenv init --path)"

Open your .bashrc with the following command

code ~/.bashrc

Add the following line.

eval "$(pyenv init -)"

To get your startup file to execute, restart your terminal.

Installing dependencies on Windows and Ubuntu

If you use macOS you can skip this step.

For Windows and Ubuntu users you will need to install some extra dependencies for python. (See here for more information about the prerequisites: pyenv Prerequities)

First run this command to update your apt repositories:

sudo apt update

and then run this command to install the packages listed on the pyenv.

sudo apt-get install -y build-essential libssl-dev zlib1g-dev libbz2-dev \
libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev libncursesw5-dev \
xz-utils tk-dev libffi-dev liblzma-dev python-openssl git

Installing python itself

Now we are ready to install python. We will be installing Python version 3.9.4.

Then run this command to install python (you'll notice pyenv makes us put in the exact version instead of being able to just say 3.9 or 3)

pyenv install 3.9.4

After some time this should complete without any errors. It could take a while since you are compiling python from source code.

Once this is finished we also need to tell pyenv this is our default version of python using this command:

pyenv global 3.9.4

Ensure that these changes take effect by closing your terminal and opening a new one. Then, we can verify our python is the correct version by typing

python --version
python3 --version

Both of these commands should show 3.9.4

Pipenv

Another piece of software we will use in class is Pipenv. Don't worry about what this is right now, it's just enough to install it.

pip install pipenv

Then after you have installed pipenv, add this line to your shell startup file (either your .bashrc or your .zshrc) somewhere after the eval "$(pyenv init -)".

export PIPENV_VENV_IN_PROJECT=1

Congratulations! If you've completed all these steps you are ready to code in Python!

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Last updated 2 years ago