Fix create_limited_print_func

diffoscope/presenters/utils.py

@@ -82,16 +82,16 @@ def make_printer(path):
         output.close()
 
 def create_limited_print_func(print_func, max_page_size):
-    count = 0
+    count = [0]
 
-    def fn(val, force=False, count=count):
+    def fn(val, force=False):
         print_func(val)
 
         if force or max_page_size == 0:
             return
 
-        count += len(val)
-        if count >= max_page_size:
+        count[0] += len(val)
+        if count[0] >= max_page_size:
             raise PrintLimitReached()
 
     return fn

tests/test_presenters.py

@@ -22,6 +22,7 @@ import re
 import pytest
 
 from diffoscope.main import main
+from diffoscope.presenters.utils import create_limited_print_func, PrintLimitReached
 
 from .utils.data import cwd_data, get_data
 
@@ -137,3 +138,16 @@ def test_html_option_with_stdout(capsys):
     out = run(capsys, '--html', '-')
 
     assert extract_body(out) == extract_body(get_data('output.html'))
+
+def test_limited_print():
+    fake = lambda x: None
+    with pytest.raises(PrintLimitReached):
+        p = create_limited_print_func(fake, 5)
+        p("123456")
+    with pytest.raises(PrintLimitReached):
+        p = create_limited_print_func(fake, 5)
+        p("123")
+        p("456")
+    p = create_limited_print_func(fake, 5)
+    p("123")
+    p("456", force=True)