Pool predictions also done for "random" heuristic

[Arthur Thuy]

Describe the bug
In the step function of the ActiveLearningLoop class, predictions on the unlabeled pool set are first performed without considering the heuristic used afterward (see lines 82-84). For the "random" heuristic, this calculation is unnecessary as pool points are selected randomly.

To Reproduce
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Expected behavior
The self.get_probabilities(pool, **self.kwargs) should not be called when the "random" heuristic is used.

One possible solution is to check the __name__ attribute of the heuristic class and to create a dummy probs array when the heuristic is random. The first dimension of this array should just have the length of the pool set.

if len(pool) > 0:
    ##### CHANGES: start #####
    if self.heuristic.__class__.__name__ == "Random":
        probs = np.random.uniform(low=0, high=1, size=(len(pool), 1))
    else:
        probs = self.get_probabilities(pool, **self.kwargs)
    ##### CHANGES: end #####
    if probs is not None and (isinstance(probs, types.GeneratorType) or len(probs) > 0):
        to_label, uncertainty = self.heuristic.get_ranks(probs)

Version (please complete the following information):

• OS: Ubuntu 20.04
• Python: 3.9.16
• Baal version: 1.8.0

Additional context
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What do you think?

I have limited experience with contributing to open source projects but I am happy to try to make a pull request.

[Frédéric Branchaud-Charron]

Fixed in #277