Builds a graph of steps.
    Args:
        steps (list): a list of :class:`Step` objects to execute.

def build_graph(steps):
    """Builds a graph of steps.
    Args:
        steps (list): a list of :class:`Step` objects to execute.
    """

    graph = Graph()

    for step in steps:
        graph.add_step(step)

    for step in steps:
        for dep in step.requires:
            graph.connect(step.name, dep)

        for parent in step.required_by:
            graph.connect(parent, step.name)

    return graph