Merge branch 'delayed-sample-from-sample' into 'master'

Add a DelayedSample.from_sample classmethod

See merge request !74

bob/pipelines/sample.py

@@ -89,7 +89,7 @@ class Sample(_ReprMixin):
         _copy_attributes(self, parent, kwargs)
 
 
-class DelayedSample(_ReprMixin):
+class DelayedSample(Sample):
     """Representation of sample that can be loaded via a callable.
 
     The optional ``**kwargs`` argument allows you to attach more attributes to
@@ -168,6 +168,26 @@ class DelayedSample(_ReprMixin):
         """Loads the data from the disk file."""
         return self._load()
 
+    @classmethod
+    def from_sample(cls, sample: Sample, **kwargs):
+        """Creates a DelayedSample from another DelayedSample or a Sample.
+        If the sample is a DelayedSample, its data will not be loaded.
+
+        Parameters
+        ----------
+
+        sample : :any:`Sample`
+            The sample to convert to a DelayedSample
+        """
+        if hasattr(sample, "_load"):
+            data = sample._load
+        else:
+
+            def data():
+                return sample.data
+
+        return cls(data, parent=sample, **kwargs)
+
 
 class SampleSet(MutableSequence, _ReprMixin):
     """A set of samples with extra attributes"""

bob/pipelines/tests/test_samples.py

@@ -117,3 +117,29 @@ def test_delayed_samples():
 
     delayed_sample.annot = "changed"
     assert delayed_sample.annot == "changed", delayed_sample.annot
+
+    # test DelayedSample.from_smaple
+
+    # check if a non-delayed sample is correctly converted to a delayed sample
+    non_delayed_sample = Sample(1)
+    delayed_sample = DelayedSample.from_sample(non_delayed_sample, annot="test")
+    assert delayed_sample.data == 1, delayed_sample.data
+    assert delayed_sample.annot == "test", delayed_sample.annot
+
+    # check if converting a delayed sample will not load the data
+    raise_error = True
+
+    def never_load():
+        if raise_error:
+            raise ValueError("never_load should not be called")
+        return 0
+
+    delayed_sample = DelayedSample(
+        never_load, delayed_attributes=dict(annot=never_load)
+    )
+    # should not raise an error when creating the delayed sample
+    child_sample = DelayedSample.from_sample(delayed_sample)
+
+    raise_error = False
+    assert child_sample.data == 0, child_sample.data
+    assert child_sample.annot == 0, child_sample.annot