Example Python repository
See here for examples of Pants's Python functionality.
Enable the Python backend like this:
[GLOBAL] ... backend_packages = [ 'pants.backend.python' ]
You should now see some new goals available:
$ ./pants help goals ... package Create a distributable package. repl Open a REPL with the specified code loadable. ... run Runs a binary target. ... test Run tests.
Have content in your
Pants automatically uses all relevant
__init__.pyfiles, even if dependency inference does not include the files and you don't add it to the
dependenciesfields of your targets.
This works if you have empty
__init__.pyfiles, like most Python projects do; but if you have actual code in your
__init__.pyfiles, you should turn on this option in your
[python-infer] inits = true
This option will cause Pants to infer "proper" dependencies on any ancestor
__init__.pyfile. If you run
./pants dependencies project/util/foo.py, you should see
project/util/__init__.pyshow up. This will ensure that any of the
__init__.pyfiles are included.
Using Python 3.8's
:=walrus operator? Tweak the
For dependency inference to work properly when using Python 3.8+ syntax, you need to tweak the
./pantsscript to run the tool with Python 3.8, rather than 3.6 or 3.7. Change the function
set_supported_python_versionsto only use 3.8: https://github.com/pantsbuild/setup/blob/2f079cbe4fc6a1d9d87decba51f19d7689aee69e/pants#L140-L141. If you do not have that function in your
./pantsscript, you likely need to update the script by copying the file from the above GitHub link.
This will be fixed in 2.2 so that Pants can always parse your code, regardless of what interpreter Pants is run with.
macOS users: you may need to change interpreter search paths
By default, Pants will look at both your
$PATHand—if you use Pyenv—your
$(pyenv root)/versionsfolder when discovering Python interpreters. Your
$PATHlikely includes the system Pythons at
/usr/bin/python3, which are known to have many issues like failing to install some dependencies.
Pants will prefer new Python versions, like 3.6.10 over 3.6.3. Because macOS system Pythons are usually very old, they will usually be ignored.
However, if you run into issues, you can set the
interpreter_search_pathsoption in the
[python-setup] interpreter_search_paths = [ # This will use all interpreters in `$(pyenv root)/versions`. "<PYENV>", # Brew usually installs Python here. "/usr/local/bin", ]
See here for more information.
Updated 3 days ago