Installing Pants

There are a few ways to get a runnable version of pants set up for your workspace. Before beginning, make sure your machine fits the requirements. At a minimum, pants requires the following to run properly:

  • Linux or Mac OS X.
  • Python 2.7.x (the latest stable version of 2.7 is recommended).
  • A C compiler, system headers, Python headers (to compile native Python modules) and the libffi library and headers (to compile and link modules that use CFFI to access native code).
  • OpenJDK or Oracle JDK 7 or greater.
  • Internet access (so that pants can fully bootstrap itself)

After you have pants installed, you'll need to Set up your code workspace to work with Pants.

To set up pants in your repo, we recommend installing our self-contained pants bash script in the root (ie, "buildroot") of your repo:

  curl -L -O https://pantsbuild.github.io/setup/pants && chmod +x pants && touch pants.ini

The first time you run the new ./pants script it will install the latest version of pants (using virtualenv) and then run it. It's recommended though, that you pin the version of pants. To do this, first find out the version of pants you just installed:

  ./pants -V
  1.0.0

Then add an entry like so to pants.ini with that version:

  [GLOBAL]
  pants_version: 1.0.0

When you'd like to upgrade pants, just edit the version in pants.ini and pants will self-update on the next run. This script stores the various pants versions you use centrally in ~/.cache/pants/setup. When you switch back and forth between branches pants will select the correct version from your local cache and use that.

If you use pants plugins published to pypi you can configure them by adding a plugins list as follows:

  [GLOBAL]
  pants_version: 1.0.0

  plugins: [
      'pantsbuild.pants.contrib.go==%(pants_version)s',
      'pantsbuild.pants.contrib.scrooge==%(pants_version)s',
    ]

Pants notices you changed your plugins and it installs them. NB: The formatting of the plugins list is important; all lines below the plugins: line must be indented by at least one white space to form logical continuation lines. This is standard for python ini files, see Options.

The ./pants Runner Script

We highly recommend invoking pants via a checked-in runner script named pants in the root of your workspace, as demonstrated above. Pants uses the presence of such a file, in the current working directory or in any of its ancestors, to detect the buildroot, e.g., when invoked in a subdirectory.

If, for whatever reason, you don't want to run pants that way, you can also just check in an empty file named pants to act as a sentinel for the buildroot.

Note that you can create whatever symlinks or extra wrapper scripts you like. There's no absolute requirement that pants be invoked directly via ./pants. All pants cares about is the existence of a file named pants in the buildroot, and that file might as well be the runner script!

PEX-based Installation

The virtualenv-based method is the recommended way of installing Pants. However in cases where you can't depend on a local pants installation (e.g., your machines prohibit software installation), some sites fetch a pre-built executable pants.pex using the pants_version defined in pants.ini. To upgrade pants, they generate a pants.pex and upload it to a file server at a location computable from the version number. They then write their own ./pants script that checks the pants_version in pants.ini and download the appropriate pex from the file server to the correct spot.

Troubleshooting

While pants is written in pure Python, some of its dependencies contain native code. Therefore, you'll need to make sure you have the appropriate compiler infrastructure installed on the machine where you are attempting to bootstrap pants. In particular, if you see an error similar to this:

Installing setuptools, pip...done.
    Command "/Users/someuser/workspace/pants/build-support/pants_deps.venv/bin/python2.7 -c "import setuptools, tokenize;__file__='/private/var/folders/zc/0jhjvzy56s723lpq23q89f6c0000gn/T/pip-build-mZzSSA/psutil/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /var/folders/zc/0jhjvzy56s723lpq23q89f6c0000gn/T/pip-iONF8p-record/install-record.txt --single-version-externally-managed --compile --install-headers /Users/someuser/workspace/pants/build-support/pants_deps.venv/bin/../include/site/python2.7/psutil" failed with error code 1 in /private/var/folders/zc/0jhjvzy56s723lpq23q89f6c0000gn/T/pip-build-mZzSSA/psutil

Failed to install requirements from /Users/someuser/workspace/pants/3rdparty/python/requirements.txt.

This indicates that pants was attempting to pip install the psutil dependency into it's private virtualenv, and that install failed due to a compiler issue. On Mac OS X, we recommend running xcode-select --install to make sure you have the latest compiler infrastructure installed, and unset any compiler-related environment variables (i.e. run unset CC).

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