skip frequent progress bar renders

CHANGES.rst

@@ -149,6 +149,8 @@ Unreleased
     type like an input value would be. :pr:`1517`
 -   Automatically generated short help messages will stop at the first
     ending of a phrase or double linebreak. :issue:`1082`
+-   Skip progress bar render steps for efficiency with very fast
+    iterators by setting ``update_min_steps``. :issue:`676`
 
 
 Version 7.1.2

src/click/_termui_impl.py

@@ -62,6 +62,7 @@ def __init__(
         label=None,
         file=None,
         color=None,
+        update_min_steps=1,
         width=30,
     ):
         self.fill_char = fill_char
@@ -77,6 +78,8 @@ def __init__(
             file = _default_text_stdout()
         self.file = file
         self.color = color
+        self.update_min_steps = update_min_steps
+        self._completed_intervals = 0
         self.width = width
         self.autowidth = width == 0
 
@@ -290,13 +293,23 @@ def update(self, n_steps, current_item=None):
         :param current_item: Optional item to set as ``current_item``
             for the updated position.
 
-        .. versionadded:: 8.0
+        .. versionchanged:: 8.0
             Added the ``current_item`` optional parameter.
+
+        .. versionchanged:: 8.0
+            Only render when the number of steps meets the
+            ``update_min_steps`` threshold.
         """
-        self.make_step(n_steps)
-        if current_item is not None:
-            self.current_item = current_item
-        self.render_progress()
+        self._completed_intervals += n_steps
+
+        if self._completed_intervals >= self.update_min_steps:
+            self.make_step(self._completed_intervals)
+
+            if current_item is not None:
+                self.current_item = current_item
+
+            self.render_progress()
+            self._completed_intervals = 0
 
     def finish(self):
         self.eta_known = 0

src/click/termui.py

@@ -299,6 +299,7 @@ def progressbar(
     width=36,
     file=None,
     color=None,
+    update_min_steps=1,
 ):
     """This function creates an iterable context manager that can be used
     to iterate over something while showing a progress bar.  It will
@@ -353,12 +354,6 @@ def progressbar(
                 archive.extract()
                 bar.update(archive.size, archive)
 
-    .. versionadded:: 2.0
-
-    .. versionadded:: 4.0
-       Added the `color` parameter.  Added a `update` method to the
-       progressbar object.
-
     :param iterable: an iterable to iterate over.  If not provided the length
                      is required.
     :param length: the number of items to iterate over.  By default the
@@ -397,6 +392,17 @@ def progressbar(
                   default is autodetection.  This is only needed if ANSI
                   codes are included anywhere in the progress bar output
                   which is not the case by default.
+    :param update_min_steps: Render only when this many updates have
+        completed. This allows tuning for very fast iterators.
+
+    .. versionadded:: 8.0
+       Added the ``update_min_steps`` parameter.
+
+    .. versionchanged:: 4.0
+        Added the ``color`` parameter. Added the ``update`` method to
+        the object.
+
+    .. versionadded:: 2.0
     """
     from ._termui_impl import ProgressBar
 
@@ -416,6 +422,7 @@ def progressbar(
         label=label,
         width=width,
         color=color,
+        update_min_steps=update_min_steps,
     )
 
 

tests/test_termui.py

@@ -344,6 +344,16 @@ def cli():
     assert "Custom 4" in lines[2]
 
 
+def test_progress_bar_update_min_steps(runner):
+    bar = _create_progress(update_min_steps=5)
+    bar.update(3)
+    assert bar._completed_intervals == 3
+    assert bar.pos == 0
+    bar.update(2)
+    assert bar._completed_intervals == 0
+    assert bar.pos == 5
+
+
 @pytest.mark.parametrize("key_char", ("h", "H", "é", "À", " ", "字", "àH", "àR"))
 @pytest.mark.parametrize("echo", [True, False])
 @pytest.mark.skipif(not WIN, reason="Tests user-input using the msvcrt module.")