Issue #26039: Document ZipInfo.is_dir() and make force_zip64 keyword-only.
Patch by Thomas Kluyver.
diff --git a/Lib/zipfile.py b/Lib/zipfile.py
index 03dead5..27a4c71 100644
--- a/Lib/zipfile.py
+++ b/Lib/zipfile.py
@@ -502,6 +502,7 @@
         return zinfo
 
     def is_dir(self):
+        """Return True if this archive member is a directory."""
         return self.filename[-1] == '/'
 
 
@@ -1343,7 +1344,7 @@
         with self.open(name, "r", pwd) as fp:
             return fp.read()
 
-    def open(self, name, mode="r", pwd=None, force_zip64=False):
+    def open(self, name, mode="r", pwd=None, *, force_zip64=False):
         """Return file-like object for 'name'.
 
         name is a string for the file name within the ZIP file, or a ZipInfo