Implemented the hash_fn mechanism into the biometric algorithm

bob/bio/base/pipelines/vanilla_biometrics/wrappers.py

@@ -49,6 +49,14 @@ class BioAlgorithmCheckpointWrapper(BioAlgorithm):
         force: bool
           If True, will recompute scores and biometric references no matter if a file exists
 
+        hash_fn
+        Pointer to a hash function. This hash function maps
+        `sample.key` to a hash code and this hash code corresponds a relative directory
+        where a single `sample` will be checkpointed.
+        This is useful when is desirable file directories with less than
+        a certain number of files.
+
+
     Examples
     --------
 
@@ -59,7 +67,13 @@ class BioAlgorithmCheckpointWrapper(BioAlgorithm):
     """
 
     def __init__(
-        self, biometric_algorithm, base_dir, group=None, force=False, **kwargs
+        self,
+        biometric_algorithm,
+        base_dir,
+        group=None,
+        force=False,
+        hash_fn=None,
+        **kwargs
     ):
         super().__init__(**kwargs)
 
@@ -70,6 +84,7 @@ class BioAlgorithmCheckpointWrapper(BioAlgorithm):
         self.force = force
         self._biometric_reference_extension = ".hdf5"
         self._score_extension = ".pickle.gz"
+        self.hash_fn = hash_fn
 
     def clear_caches(self):
         self.biometric_algorithm.clear_caches()
@@ -109,10 +124,16 @@ class BioAlgorithmCheckpointWrapper(BioAlgorithm):
         """
 
         # Amending `models` directory
+        hash_dir_name = (
+            self.hash_fn(str(sampleset.key)) if self.hash_fn is not None else ""
+        )
+
         path = os.path.join(
             self.biometric_reference_dir,
+            hash_dir_name,
             str(sampleset.key) + self._biometric_reference_extension,
         )
+
         if self.force or not os.path.exists(path):
 
             enrolled_sample = self.biometric_algorithm._enroll_sample_set(sampleset)
@@ -147,8 +168,14 @@ class BioAlgorithmCheckpointWrapper(BioAlgorithm):
             suffix = "_".join([str(s.key) for s in biometric_references[0:3]])
             return os.path.join(reference_id, name + suffix)
 
+        # Amending `models` directory
+        hash_dir_name = (
+            self.hash_fn(str(sampleset.key)) if self.hash_fn is not None else ""
+        )
+
         path = os.path.join(
             self.score_dir,
+            hash_dir_name,
             _make_name(sampleset, biometric_references) + self._score_extension,
         )
 
@@ -333,7 +360,7 @@ def checkpoint_vanilla_biometrics(
         pipeline.biometric_algorithm.base_dir = bio_ref_scores_dir
     else:
         pipeline.biometric_algorithm = BioAlgorithmCheckpointWrapper(
-            pipeline.biometric_algorithm, base_dir=bio_ref_scores_dir
+            pipeline.biometric_algorithm, base_dir=bio_ref_scores_dir, hash_fn=hash_fn
         )
 
     return pipeline