4.12.13.1 Writing BuildStep Constructors

BuildStep classes have some extra equipment, because they are their own factories. Consider the use of a BuildStep in master.cfg:

     f.addStep(MyStep(someopt="stuff", anotheropt=1))

This creates a single instance of class MyStep. However, Buildbot needs a new object each time the step is executed. this is accomplished by storing the information required to instantiate a new object in the factory attribute. When the time comes to construct a new Build, BuildFactory consults this attribute (via getStepFactory) and instantiates a new step object.

When writing a new step class, then, keep in mind are that you cannot do anything "interesting" in the constructor – limit yourself to checking and storing arguments. To ensure that these arguments are provided to any new objects, call self.addFactoryArguments with any keyword arguments your constructor needs.

Keep a **kwargs argument on the end of your options, and pass that up to the parent class's constructor.

The whole thing looks like this:

     class Frobinfy(LoggingBuildStep):
         def __init__(self,
                 frob_what="frobee",
                 frob_how_many=None,
                 frob_how=None,
                 **kwargs):
     
             # check
             if frob_how_many is None:
                 raise TypeError("Frobinfy argument how_many is required")
     
             # call parent
             LoggingBuildStep.__init__(self, **kwargs)
     
             # set Frobnify attributes
             self.frob_what = frob_what
             self.frob_how_many = how_many
             self.frob_how = frob_how
     
             # and record arguments for later
             self.addFactoryArguments(
                 frob_what=frob_what,
                 frob_how_many=frob_how_many,
                 frob_how=frob_how)
     
     class FastFrobnify(Frobnify):
         def __init__(self,
                 speed=5,
                 **kwargs)
             Frobnify.__init__(self, **kwargs)
             self.speed = speed
             self.addFactoryArguments(
                 speed=speed)