builder, build_state, source, prog)
This event is emitted right before a source is being built into a final build artifact. Note that this event in itself does not indicate if the build will actually take place or not due to the artifact being current already as such the usefulness is limited.
The parameters being passed are:
builder: a reference to the builder.
build_state: a reference to the build state object.
source: the source object that is being processed. (See Source Object for more information)
prog: the build program that is being used to process the source. (See Build Program for more information)
Note that currently both the builder as well as the build state are undocumented and unsupported! This means that if a plugin choses to use those references to do something with it they should consider that they might break in future versions.
def on_before_build(self, source, prog, **extra): print('building %s' % source.source_filename)