diff --git a/nipype/info.py b/nipype/info.py
index 284fe4101b..7b68ec909c 100644
--- a/nipype/info.py
+++ b/nipype/info.py
@@ -187,7 +187,7 @@ def get_nipype_gitversion():
 
 
 def _list_union(iterable):
-    return list(set(sum(iterable, [])))
+    return list(set(x for sublist in iterable for x in sublist))
 
 
 # Enable a handle to install all extra dependencies at once
diff --git a/nipype/interfaces/fsl/utils.py b/nipype/interfaces/fsl/utils.py
index acdd771fc8..2cf868371d 100644
--- a/nipype/interfaces/fsl/utils.py
+++ b/nipype/interfaces/fsl/utils.py
@@ -483,7 +483,7 @@ class ExtractROI(FSLCommand):
 
     def _format_arg(self, name, spec, value):
         if name == "crop_list":
-            return " ".join(map(str, sum(list(map(list, value)), [])))
+            return " ".join(str(x) for sublist in value for x in sublist)
         return super()._format_arg(name, spec, value)
 
     def _list_outputs(self):
diff --git a/nipype/interfaces/spm/base.py b/nipype/interfaces/spm/base.py
index e6b898c78b..4998f0af34 100644
--- a/nipype/interfaces/spm/base.py
+++ b/nipype/interfaces/spm/base.py
@@ -52,7 +52,7 @@ def func_is_3d(in_file):
     else:
         img = load(in_file)
         shape = img.shape
-        return len(shape) == 3 or len(shape) == 4 and shape[3] == 1
+        return len(shape) == 3 or (len(shape) == 4 and shape[3] == 1)
 
 
 def get_first_3dfile(in_files):