fix: remove trailing underscore from output filenames

Fixes #1389

Removed the unnecessary trailing underscore from output filenames.
- Old format: ComfyUI_00001_.png
- New format: ComfyUI_00001.png

Updated get_save_image_path to support both formats for backward
compatibility with existing files.

folder_paths.py

@@ -430,7 +430,11 @@ def get_save_image_path(filename_prefix: str, output_dir: str, image_width=0, im
         prefix_len = len(os.path.basename(filename_prefix))
         prefix = filename[:prefix_len + 1]
         try:
-            digits = int(filename[prefix_len + 1:].split('_')[0])
+            # Extract the part after prefix (e.g., "00001_.png" or "00001.png")
+            remainder = filename[prefix_len + 1:]
+            # Try to parse digits - handle both "00001_" and "00001." formats
+            digits_str = remainder.split('_')[0].split('.')[0]
+            digits = int(digits_str)
         except:
             digits = 0
         return digits, prefix
@@ -464,7 +468,18 @@ def get_save_image_path(filename_prefix: str, output_dir: str, image_width=0, im
         raise Exception(err)
 
     try:
-        counter = max(filter(lambda a: os.path.normcase(a[1][:-1]) == os.path.normcase(filename) and a[1][-1] == "_", map(map_filename, os.listdir(full_output_folder))))[0] + 1
+        # Support both old format (filename_) and new format (filename) for backward compatibility
+        def matches_filename(a):
+            prefix = a[1]
+            # Match new format: "filename" (exact match)
+            if os.path.normcase(prefix) == os.path.normcase(filename):
+                return True
+            # Match old format: "filename_" (with trailing underscore)
+            if prefix.endswith("_") and os.path.normcase(prefix[:-1]) == os.path.normcase(filename):
+                return True
+            return False
+
+        counter = max(filter(lambda a: matches_filename(a), map(map_filename, os.listdir(full_output_folder))))[0] + 1
     except ValueError:
         counter = 1
     except FileNotFoundError:

nodes.py

@@ -488,7 +488,7 @@ class SaveLatent:
                 for x in extra_pnginfo:
                     metadata[x] = json.dumps(extra_pnginfo[x])
 
-        file = f"{filename}_{counter:05}_.latent"
+        file = f"{filename}_{counter:05}.latent"
 
         results: list[FileLocator] = []
         results.append({
@@ -1615,7 +1615,7 @@ class SaveImage:
                         metadata.add_text(x, json.dumps(extra_pnginfo[x]))
 
             filename_with_batch_num = filename.replace("%batch_num%", str(batch_number))
-            file = f"{filename_with_batch_num}_{counter:05}_.png"
+            file = f"{filename_with_batch_num}_{counter:05}.png"
             img.save(os.path.join(full_output_folder, file), pnginfo=metadata, compress_level=self.compress_level)
             results.append({
                 "filename": file,

tests-unit/folder_paths_test/test_filename_format.py

@@ -0,0 +1,91 @@
+"""Tests for output filename format.
+
+Relates to issue #1389: Trailing underscore in output file names
+"""
+
+import os
+import tempfile
+import pytest
+
+import folder_paths
+
+
+class TestFilenameFormat:
+    """Test output filename format without trailing underscore."""
+
+    def test_new_filename_format_no_trailing_underscore(self):
+        """New files should not have trailing underscore before extension."""
+        # Expected format: "prefix_00001.png" not "prefix_00001_.png"
+        filename = "ComfyUI"
+        counter = 1
+        new_format = f"{filename}_{counter:05}.png"
+
+        assert new_format == "ComfyUI_00001.png"
+        assert not new_format.endswith("_.png"), "Filename should not have trailing underscore"
+
+    def test_get_save_image_path_backward_compatible(self):
+        """get_save_image_path should work with both old and new format files."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            # Create files with old format (trailing underscore)
+            old_format_files = [
+                "TestPrefix_00001_.png",
+                "TestPrefix_00002_.png",
+            ]
+            for f in old_format_files:
+                open(os.path.join(tmpdir, f), 'w').close()
+
+            # get_save_image_path should recognize old format and return next counter
+            full_path, filename, counter, subfolder, _ = folder_paths.get_save_image_path(
+                "TestPrefix", tmpdir
+            )
+
+            # Counter should be 3 (after 00001 and 00002)
+            assert counter == 3
+
+    def test_get_save_image_path_new_format(self):
+        """get_save_image_path should work with new format files (no trailing underscore)."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            # Create files with new format (no trailing underscore)
+            new_format_files = [
+                "NewPrefix_00001.png",
+                "NewPrefix_00002.png",
+                "NewPrefix_00003.png",
+            ]
+            for f in new_format_files:
+                open(os.path.join(tmpdir, f), 'w').close()
+
+            # get_save_image_path should recognize new format
+            full_path, filename, counter, subfolder, _ = folder_paths.get_save_image_path(
+                "NewPrefix", tmpdir
+            )
+
+            # Counter should be 4 (after 00001, 00002, 00003)
+            assert counter == 4
+
+    def test_get_save_image_path_mixed_formats(self):
+        """get_save_image_path should handle mixed old and new format files."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            # Mix of old and new format files
+            files = [
+                "MixedPrefix_00001_.png",  # old format
+                "MixedPrefix_00002.png",   # new format
+                "MixedPrefix_00003_.png",  # old format
+            ]
+            for f in files:
+                open(os.path.join(tmpdir, f), 'w').close()
+
+            full_path, filename, counter, subfolder, _ = folder_paths.get_save_image_path(
+                "MixedPrefix", tmpdir
+            )
+
+            # Counter should be 4 (recognizing both formats)
+            assert counter == 4
+
+    def test_get_save_image_path_empty_directory(self):
+        """get_save_image_path should return counter 1 for empty directory."""
+        with tempfile.TemporaryDirectory() as tmpdir:
+            full_path, filename, counter, subfolder, _ = folder_paths.get_save_image_path(
+                "EmptyDir", tmpdir
+            )
+
+            assert counter == 1