Remove single dispatch version of calculate_downsample

src/ocrmypdf/imageops.py

@@ -6,7 +6,6 @@
 from __future__ import annotations
 
 import logging
-from functools import singledispatch
 from math import floor, sqrt
 from typing import Optional, Tuple
 
@@ -43,8 +42,7 @@ def bytes_per_pixel(mode: str) -> int:
     return 4
 
 
-@singledispatch
-def calculate_downsample(
+def _calculate_downsample(
     image_size: Tuple[int, int],
     bytes_per_pixel: int,
     *,
@@ -105,10 +103,8 @@ def calculate_downsample(
     return size
 
 
-@calculate_downsample.register
-def _(
+def calculate_downsample(
     image: Image.Image,
-    arg: None = None,
     *,
     max_size: Optional[Tuple[int, int]] = None,
     max_pixels: Optional[int] = None,
@@ -126,7 +122,7 @@ def _(
         max_bytes: The maximum number of bytes in the image. RGB is counted as 4
             bytes; all other modes are counted as 1 byte.
     """
-    return calculate_downsample(
+    return _calculate_downsample(
         image.size,
         bytes_per_pixel(image.mode),
         max_size=max_size,

tests/test_imageops.py

@@ -7,7 +7,12 @@ import hypothesis.strategies as st
 from hypothesis import given
 from PIL import Image
 
-from ocrmypdf.imageops import bytes_per_pixel, calculate_downsample, downsample_image
+from ocrmypdf.imageops import (
+    _calculate_downsample,
+    bytes_per_pixel,
+    calculate_downsample,
+    downsample_image,
+)
 
 
 def test_bytes_per_pixel():
@@ -34,7 +39,7 @@ def test_calculate_downsample():
     st.integers(min_value=64 * 64, max_value=1000000),
 )
 def test_calculate_downsample_hypothesis(mode, im_w, im_h, max_x, max_y, max_bytes):
-    result = calculate_downsample(
+    result = _calculate_downsample(
         (im_w, im_h),
         bytes_per_pixel(mode),
         max_size=(max_x, max_y),