Vanilla Biometrics callback

This is a TF callback that calls vanilla-biometrics when on_epoch_end is triggered.

I know that bob.bio.base would be a better fit for it, but I didn't want to impose a TF dependency on it. Since this is, so far, used only for face recognition, I'm adding this here

bob/bio/face/tensorflow/callbacks.py

+#!/usr/bin/env python
+# coding: utf-8
+
+"""
+Some TF callbacks
+"""
+
+import tensorflow as tf
+from click.testing import CliRunner
+from bob.bio.base.script.vanilla_biometrics import vanilla_biometrics
+import logging
+import bob.measure
+import bob.bio.base
+import os
+
+logger = logging.getLogger(__name__)
+
+
+class VanillaBiometricsCallback(tf.keras.callbacks.Callback):
+    def __init__(self, config, output_path, name="vanilla-biometrics", fmr=0.001):
+        """
+        Callback that calls `bob bio pipelines vanilla-biometrics` at every `on_epoch_end`.
+        FNMR@FMR=fmr is reported at every epoch
+        
+
+        Parameters
+        ----------
+           
+           config: str
+             Path containing the `bob bio pipelines vanilla-biometrics` input script.
+             Please, check :any:`bob.bio.base.vanilla_biometrics_intro` on how to setup the 
+
+           output_path: str
+             Path where the checkpoiny is being written
+             
+           fmr: float
+              False match rate threshold that will be used to compute FNRM
+
+        """
+        self.config = config
+        self.fmr = fmr
+        self.output_path = output_path
+        self.scores_dev = os.path.join(output_path, "scores-dev")
+        super(VanillaBiometricsCallback, self).__init__()
+
+    def on_epoch_end(self, epoch, logs=None):
+        logger.info(f"Run vanilla biometrics {epoch}. Input script: {self.config}")
+
+        vanilla_biometrics.main(
+            [self.config],
+            prog_name="bob bio pipelines vanilla-biometrics",
+            standalone_mode=False,
+        )
+
+        neg, pos = bob.bio.base.score.load.split_four_column(self.scores_dev)
+        far_thres = bob.measure.far_threshold(neg, pos, self.fmr)
+        fmr, fnmr = bob.measure.fprfnr(neg, pos, far_thres)
+
+        logs[f"FNMR-at-FAR={self.fmr}"] = fnmr
+