fix: draw the download bar on a terminal only

scripts/download.py

@@ -194,9 +194,13 @@ def download_file(
         url, headers={"User-Agent": "retrobios-downloader/1.0"}
     )
 
+    # A redrawn bar only on a terminal: written to a log, 32,768 redraws of a
+    # 2 GiB part made one line of nearly 3 MB.
+    live = sys.stdout.isatty() and os.environ.get("TERM") != "dumb"
     with urllib.request.urlopen(req, timeout=300) as resp:
         total = int(resp.headers.get("Content-Length", expected_size))
         downloaded = 0
+        shown = -1
 
         with open(dest, "wb") as f:
             while True:
@@ -206,16 +210,21 @@ def download_file(
                 f.write(chunk)
                 downloaded += len(chunk)
 
-                if total > 0:
+                if total > 0 and live:
                     pct = downloaded * 100 // total
-                    bar = "=" * (pct // 2) + " " * (50 - pct // 2)
-                    print(
-                        f"\r  {label}[{bar}] {pct}% ({downloaded:,}/{total:,})",
-                        end="",
-                        flush=True,
-                    )
+                    if pct != shown:
+                        shown = pct
+                        bar = "=" * (pct // 2) + " " * (50 - pct // 2)
+                        print(
+                            f"\r  {label}[{bar}] {pct}% ({downloaded:,}/{total:,})",
+                            end="",
+                            flush=True,
+                        )
 
-    print()
+    if live:
+        print()
+    else:
+        print(f"  {label}{downloaded:,} bytes")
     if expected_size and downloaded != expected_size:
         raise ValueError(f"downloaded {downloaded} bytes; expected {expected_size}")
 

tests/test_download.py

@@ -583,5 +583,39 @@ class TestZipPartsShell(ZipPartsTests, ZipPartsCase, TestDownloadShell):
     pass
 
 
+
+class AProgressBarOnlyOnATerminal(unittest.TestCase):
+    """Redirected to a log, download.py wrote a carriage-return redraw per
+    64 KiB block: one line of nearly 3 MB for a 2 GiB part."""
+
+    def test_a_log_gets_one_line(self):
+        import contextlib
+        import io as _io
+        import tempfile as _tempfile
+        from pathlib import Path as _Path
+        from unittest import mock
+
+        import download
+
+        class Body(_io.BytesIO):
+            headers = {"Content-Length": str(200_000)}
+
+            def __enter__(self):
+                return self
+
+            def __exit__(self, *exc):
+                return False
+
+        out = _io.StringIO()
+        with _tempfile.TemporaryDirectory() as directory, \
+                mock.patch.object(download.urllib.request, "urlopen",
+                                  lambda *a, **k: Body(b"x" * 200_000)), \
+                contextlib.redirect_stdout(out):
+            download.download_file("https://example.com/a.zip",
+                                   _Path(directory) / "a.zip", 200_000, "a.zip ")
+        self.assertNotIn("\r", out.getvalue())
+        self.assertEqual(out.getvalue().count("\n"), 1)
+
+
 if __name__ == "__main__":
     unittest.main()