diff --git a/manimlib/utils/strings.py b/manimlib/utils/strings.py
index b986577d21..20612a25eb 100644
--- a/manimlib/utils/strings.py
+++ b/manimlib/utils/strings.py
@@ -4,17 +4,20 @@
 
 
 def to_camel_case(name):
-    return "".join([
-        [c for c in part if c not in string.punctuation + string.whitespace].capitalize()
-        for part in name.split("_")
-    ])
+    return "".join(
+        [
+            [
+                c for c in part if c not in string.punctuation + string.whitespace
+            ].capitalize()
+            for part in name.split("_")
+        ]
+    )
 
 
-def initials(name, sep_values=[" ", "_"]):
-    return "".join([
-        (s[0] if s else "")
-        for s in re.split("|".join(sep_values), name)
-    ])
+def initials(name, sep_values=None):
+    if sep_values is None:
+        sep_values = [" ", "_"]
+    return "".join([(s[0] if s else "") for s in re.split("|".join(sep_values), name)])
 
 
 def camel_case_initials(name):
@@ -37,10 +40,16 @@ def split_string_to_isolate_substrings(full_string, *substrings_to_isolate):
     if len(substrings_to_isolate) == 0:
         return [full_string]
     substring_to_isolate = substrings_to_isolate[0]
-    all_substrings = list(it.chain(*list(zip(
-        full_string.split(substring_to_isolate),
-        it.repeat(substring_to_isolate)
-    ))))
+    all_substrings = list(
+        it.chain(
+            *list(
+                zip(
+                    full_string.split(substring_to_isolate),
+                    it.repeat(substring_to_isolate),
+                )
+            )
+        )
+    )
     all_substrings.pop(-1)
     all_substrings = [s for s in all_substrings if s != ""]
     return split_string_list_to_isolate_substrings(
@@ -53,7 +62,11 @@ def split_string_list_to_isolate_substrings(string_list, *substrings_to_isolate)
     Similar to split_string_to_isolate_substrings, but the first argument
     is a list of strings, thought of as something already broken up a bit.
     """
-    return list(it.chain(*[
-        split_string_to_isolate_substrings(s, *substrings_to_isolate)
-        for s in string_list
-    ]))
+    return list(
+        it.chain(
+            *[
+                split_string_to_isolate_substrings(s, *substrings_to_isolate)
+                for s in string_list
+            ]
+        )
+    )