example-python

An example repository to demonstrate Python support in Pants.

See pantsbuild.org for much more detailed documentation.

Running Pants

You run Pants goals using the ./pants wrapper script, which will bootstrap the configured version of Pants if necessary.

Use ./pants --version to see the version of Pants configured for the repo (which you can also find in pants.toml).

Goals

Pants commands are called goals. You can get a list of goals with

./pants goals

Targets

Targets are sets of source files with some attached metadata. Targets are provided in BUILD files. Targets have types, such as python_library, resources, python_binary. Examples of metadata include dependencies on other targets, Python version compatibility, entry points for binaries, and so on.

Pants goals can be invoked on targets or directly on source files/directories (which is often more intuitive and convenient). In the latter case, Pants locates target metadata for the source files as needed.

File specifications

Invoking goals on files is straightforward, e.g.,

./pants test helloworld/util/lang_test.py

You can use globs:

./pants lint helloworld/util/*.py

But note that these will be expanded by your shell, so this is equivalent to having used

./pants lint helloworld/util/lang.py helloworld/util/lang_test.py helloworld/util/resources.py helloworld/util/resources_test.py

If you want Pants itself to expand the globs (which is sometimes necessary), you must quote them in the shell:

./pants lint 'helloworld/util/*.py'

You can run on all changed files:

./pants --changed-since=HEAD lint

You can run on all changed files, and any of their "dependees":

./pants --changed-since=HEAD --changed-dependees=transitive test

Target specifications

Targets are referenced on the command line using their address, of the form path/to/dir:name, e.g.,

./pants lint helloworld/util:util

You can omit the target name if it is the same as the immediately enclosing directory name, e.g.,

./pants lint helloworld/util

You can glob over all targets in a directory with a single trailing :, or over all targets in a directory and all its subdirectories with a double trailing ::, e.g.,

./pants lint helloworld::

Globbing semantics

When you glob over files or targets, Pants knows to ignore ones that aren't relevant to the requested goal. For example, if you run the test goal over a set of files that includes non-test files, Pants will just ignore those, rather than error. So you can safely do things like

./pants test ::

To run all tests.

In some cases trying to run a goal on multiple files or targets will fail due to conflicts. For example, you cannot ./pants repl helloworld:: because that globs over both Python 2 and Python 3 code, so there is no way to select an interpreter compatible with both both to run the REPL on.

Example Goals

Try these out in this repo!

List targets

./pants list ::  # All targets.
./pants list 'helloworld/**/*.py'  # Just targets containing Python code.

Run linters and formatters

./pants lint ::
./pants fmt 'helloworld/**/*.py'

Run MyPy

./pants typecheck ::

Run tests

./pants test ::  # Run all tests in the repo.
./pants test helloworld/util:test  # Run all the tests in this target.
./pants test helloworld/util/lang_test.py  # Run just the tests in this file.
./pants test helloworld/util/lang_test.py -- -k test_language_translator  # Run just this one test.

Create a PEX binary

./pants package helloworld/main.py helloworld/main_py2.py

Run a binary

./pants run helloworld/main.py

Open a REPL

./pants repl helloworld/greet  # The REPL will have all relevant code and dependencies on its sys.path.
./pants repl --shell=ipython helloworld/greet

Build a wheel / generate setup.py

This will build both a .whl bdist and a .tar.gz sdist.

./pants package helloworld/util:dist

We can also remove the setup_py_commands field from helloworld/util/BUILD to have Pants instead generate a setup.py file, with all the relevant code in a chroot.

Build an AWS Lambda

(This example only works on Linux because it has an sdist. See https://www.pantsbuild.org/docs/awslambda-python.)

./pants package helloworld:helloworld-awslambda

Count lines of code

./pants count-loc '**/*'