Bazel Gazelle Python Extension

Gazelle is an extensible BUILD file generator for Bazel. This repository extends Gazelle for generating Bazel rules for Python code.

This is currently experimental and is meant as an alternative to the pseudo-official option.

Salient Differences

1. Written in pure Go with more idiomatic Go code. Consequently:
   1. Uses go-python/gpython to parse Python files, which follows the specs of Python 3.4.
   2. Assumes a fixed list of root packages available with the interpreter, i.e. stdlib and other system installed packages. The list can be overridden through command line flags and directives.
2. Finer grained dependencies where modules are the build units not packages, this allows for better test caching and has better fidelity to Python build tooling.
3. Simpler infrastructure. Try to keep the focus on the logic in python/module.go and python/analyzer.go.

Wishlist

1. Collapse cyclical dependencies, at least within a single package, to a single py_library rule. Currently, the sources and their direct deps are transferred up the chain. This should be doable with a little more work.
2. Include/exclude dependencies for specific rules through directives.
3. Design a better structured format for inputs, like for external modules map and internal modules list.
4. Parse global symbols out of a Python module without loading the module to improve the accuracy of resolution of IMPORT-FROM statemetns. This may be impossible or unreliable.
5. For binary distribution wheels, extract imports from compiled modules (.so files). This may be impossible or unreliable.

Usage

Currently meant for usage by advanced users only. See configuration.go for command line flags and directives.