ENH: Add strict mode to BIDSDataGrabber

Author: effigies

nipype/interfaces/io.py

@@ -2755,6 +2755,8 @@ class BIDSDataGrabberInputSpec(DynamicTraitedSpec):
                                  desc='Generate exception if list is empty '
                                  'for a given field')
     return_type = traits.Enum('file', 'namedtuple', usedefault=True)
+    strict = traits.Bool(desc='Return only BIDS "proper" files (e.g., '
+                              'ignore derivatives/, sourcedata/, etc.)')
 
 
 class BIDSDataGrabber(IOBase):
@@ -2828,8 +2830,10 @@ def _run_interface(self, runtime):
         return runtime
 
     def _list_outputs(self):
-        layout = gb.BIDSLayout(self.inputs.base_dir,
-                               exclude=['derivatives/', 'code/', 'sourcedata/'])
+        exclude = None
+        if self.inputs.strict:
+            exclude = ['derivatives/', 'code/', 'sourcedata/']
+        layout = gb.BIDSLayout(self.inputs.base_dir, exclude=exclude)
 
         # If infield is not given nm input value, silently ignore
         filters = {}