userNameToFileName should not have a mutable default parameter

fonttools · Oct 7, 2021 · 31c3409 · 31c3409
1 parent a7e4d86
commit 31c3409
Showing 1 changed file with 3 additions and 3 deletions.
diff --git a/Lib/fontTools/ufoLib/filenames.py b/Lib/fontTools/ufoLib/filenames.py
@@ -15,9 +15,9 @@ class NameTranslationError(Exception):
 	pass
 
 
-def userNameToFileName(userName: str, existing=set(), prefix="", suffix=""):
+def userNameToFileName(userName: str, existing=None, prefix="", suffix=""):
 	"""
-	existing should be a case-insensitive list
+	existing should be a case-insensitive set
 	of all existing file names.
 
 	>>> userNameToFileName("a") == "a"
@@ -98,7 +98,7 @@ def userNameToFileName(userName: str, existing=set(), prefix="", suffix=""):
 	userName = ".".join(parts)
 	# test for clash
 	fullName = prefix + userName + suffix
-	if fullName.lower() in existing:
+	if existing is not None and fullName.lower() in existing:
 		fullName = handleClash1(userName, existing, prefix, suffix)
 	# finished
 	return fullName