wolph · wolph · Sep 30, 2019 · Sep 19, 2019
diff --git a/examples.py b/examples.py
@@ -31,6 +31,19 @@ def wrapped():
    return wrapped


+@example
+def fast_example():
+    ''' Updates bar really quickly to cause flickering '''
+    with progressbar.ProgressBar(max_value=1, widgets=[progressbar.Bar()]) as bar:
+        start = time.time()
+        while True:
+            elapsed = time.time() - start
+            if elapsed > 1:
+                break
+            else:
+                bar.update(elapsed, force=True)
+
+
 @example
 def shortcut_example():
    for i in progressbar.progressbar(range(10)):

diff --git a/progressbar/bar.py b/progressbar/bar.py
@@ -180,9 +180,10 @@ def start(self, *args, **kwargs):
        DefaultFdMixin.start(self, *args, **kwargs)

    def update(self, value=None):
-        if not self.line_breaks:
-            self.fd.write('\r' + ' ' * self.term_width + '\r')
-        utils.streams.flush()
+        if utils.streams.needs_flush():
+            if not self.line_breaks:
+                self.fd.write('\r' + ' ' * self.term_width + '\r')
+            utils.streams.flush()
        DefaultFdMixin.update(self, value=value)

    def finish(self, end='\n'):

diff --git a/progressbar/utils.py b/progressbar/utils.py
@@ -135,6 +135,9 @@ def write(self, value):
    def flush(self):
        self.buffer.flush()

+    def _needs_flush(self):
+        return bool(self.buffer.getvalue())
+
    def _flush(self):
        value = self.buffer.getvalue()
        if value:
@@ -249,6 +252,15 @@ def unwrap_stderr(self):
            sys.stderr = self.original_stderr
            self.wrapped_stderr = 0

+    def needs_flush(self):
+        if self.wrapped_stdout:
+            if self.stdout._needs_flush():
+                return True
+        if self.wrapped_stderr:
+            if self.stderr._needs_flush():
+              return True
+        return False
+
    def flush(self):
        if self.wrapped_stdout:  # pragma: no branch
            try: