Add simple download progress option

docs/html/user_guide.rst

@@ -856,6 +856,12 @@ We are using `freeze`_ here which outputs installed packages in requirements for
 
   reqs = subprocess.check_output([sys.executable, '-m', 'pip', 'freeze'])
 
+To programmatically monitor download progress use the ``--progress-bar=raw`` option.
+This will print lines to stdout in the format ``Progress CURRENT of TOTAL``, where
+``CURRENT`` and ``TOTAL`` are integers and the unit is bytes.
+If the real total is unknown then ``TOTAL`` is set to ``0``. Be aware that the
+specific formatting of pip's outputs are *not* guaranteed to be the same in future versions.
+
 If you don't want to use pip's command line functionality, but are rather
 trying to implement code that works with Python packages, their metadata, or
 PyPI, then you should consider other, supported, packages that offer this type

news/11508.feature.rst

@@ -0,0 +1 @@
+Add a 'raw' progress_bar type for simple and parsable download progress reports

src/pip/_internal/cli/cmdoptions.py

@@ -226,9 +226,9 @@ class PipOption(Option):
     "--progress-bar",
     dest="progress_bar",
     type="choice",
-    choices=["on", "off"],
+    choices=["on", "off", "raw"],
     default="on",
-    help="Specify whether the progress bar should be used [on, off] (default: on)",
+    help="Specify whether the progress bar should be used [on, off, raw] (default: on)",
 )
 
 log: Callable[..., Option] = partial(

src/pip/_internal/cli/progress_bars.py

@@ -1,4 +1,5 @@
 import functools
+import sys
 from typing import Callable, Generator, Iterable, Iterator, Optional, Tuple
 
 from pip._vendor.rich.progress import (
@@ -14,6 +15,7 @@
     TransferSpeedColumn,
 )
 
+from pip._internal.cli.spinners import RateLimiter
 from pip._internal.utils.logging import get_indentation
 
 DownloadProgressRenderer = Callable[[Iterable[bytes]], Iterator[bytes]]
@@ -55,6 +57,28 @@ def _rich_progress_bar(
             progress.update(task_id, advance=len(chunk))
 
 
+def _raw_progress_bar(
+    iterable: Iterable[bytes],
+    *,
+    size: Optional[int],
+) -> Generator[bytes, None, None]:
+    def write_progress(current: int, total: int) -> None:
+        sys.stdout.write("Progress %d of %d\n" % (current, total))
+        sys.stdout.flush()
+
+    current = 0
+    total = size or 0
+    rate_limiter = RateLimiter(0.25)
+
+    write_progress(current, total)
+    for chunk in iterable:
+        current += len(chunk)
+        if rate_limiter.ready() or current == total:
+            write_progress(current, total)
+            rate_limiter.reset()
+        yield chunk
+
+
 def get_download_progress_renderer(
     *, bar_type: str, size: Optional[int] = None
 ) -> DownloadProgressRenderer:
@@ -64,5 +88,7 @@ def get_download_progress_renderer(
     """
     if bar_type == "on":
         return functools.partial(_rich_progress_bar, bar_type=bar_type, size=size)
+    elif bar_type == "raw":
+        return functools.partial(_raw_progress_bar, size=size)
     else:
         return iter  # no-op, when passed an iterator