diff --git a/nipype/pipeline/engine/utils.py b/nipype/pipeline/engine/utils.py
index 0e27bdcd2b..3601290cd9 100644
--- a/nipype/pipeline/engine/utils.py
+++ b/nipype/pipeline/engine/utils.py
@@ -1489,10 +1489,9 @@ def clean_working_directory(
                     files2remove.append(f)
     else:
         if not str2bool(config["execution"]["keep_inputs"]):
-            input_files = []
-            inputdict = inputs.trait_get()
-            input_files.extend(walk_outputs(inputdict))
-            input_files = [path for path, type in input_files if type == "f"]
+            input_files = {
+                path for path, type in walk_outputs(inputs.trait_get()) if type == "f"
+            }
             files2remove.extend(
                 f for f in walk_files(cwd) if f in input_files and f not in needed_files
             )
diff --git a/nipype/utils/filemanip.py b/nipype/utils/filemanip.py
index adde6f75a5..e97b93c3f9 100644
--- a/nipype/utils/filemanip.py
+++ b/nipype/utils/filemanip.py
@@ -444,16 +444,15 @@ def get_related_files(filename, include_this_file=True):
     include_this_file : bool
         If true, output includes the input filename.
     """
-    related_files = []
     path, name, this_type = split_filename(filename)
-    for type_set in related_filetype_sets:
-        if this_type in type_set:
-            related_files.extend(
-                op.join(path, name + related_type)
-                for related_type in type_set
-                if include_this_file or related_type != this_type
-            )
-    if not len(related_files):
+    related_files = [
+        op.join(path, f"{name}{related_type}")
+        for type_set in related_filetype_sets
+        if this_type in type_set
+        for related_type in type_set
+        if include_this_file or related_type != this_type
+    ]
+    if not related_files:
         related_files = [filename]
     return related_files
 
@@ -715,13 +714,11 @@ def write_rst_header(header, level=0):
 
 
 def write_rst_list(items, prefix=""):
-    out = [f"{prefix} {item}" for item in ensure_list(items)]
-    return "\n".join(out) + "\n\n"
+    return "\n".join(f"{prefix} {item}" for item in ensure_list(items)) + "\n\n"
 
 
 def write_rst_dict(info, prefix=""):
-    out = [f"{prefix}* {key} : {value}" for key, value in sorted(info.items())]
-    return "\n".join(out) + "\n\n"
+    return "\n".join(f"{prefix}* {k} : {v}" for k, v in sorted(info.items())) + "\n\n"
 
 
 def dist_is_editable(dist):
diff --git a/nipype/utils/nipype2boutiques.py b/nipype/utils/nipype2boutiques.py
index 0309263aa5..90785f447e 100644
--- a/nipype/utils/nipype2boutiques.py
+++ b/nipype/utils/nipype2boutiques.py
@@ -477,7 +477,7 @@ def get_boutiques_output(outputs, name, spec, interface, tool_inputs):
             # If extensions all the same, set path template as
             # wildcard + extension. Otherwise just use a wildcard
             if len(extensions) == 1:
-                output["path-template"] = "*" + extensions[0]
+                output["path-template"] = "*" + extensions.pop()
             else:
                 output["path-template"] = "*"
             return output