From a112bb200a54727fa5f4d72e994ca6aaf8b4a553 Mon Sep 17 00:00:00 2001
From: Robert Graham <rpgraham84@gmail.com>
Date: Tue, 15 May 2018 15:25:08 -0400
Subject: [PATCH] Fixes issue #447

Fixes a ZeroDivisionError in ProgressBar.make_step when the first
arg passed to the first call of ProgressBar.update is 0.
---
 click/_termui_impl.py | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/click/_termui_impl.py b/click/_termui_impl.py
index 0c815a25d..0b39731cd 100644
--- a/click/_termui_impl.py
+++ b/click/_termui_impl.py
@@ -245,7 +245,16 @@ def make_step(self, n_steps):
             return
 
         self.last_eta = time.time()
-        self.avg = self.avg[-6:] + [-(self.start - time.time()) / (self.pos)]
+
+        # self.avg is a rolling list of length <= 7 of steps where steps are
+        # defined as time elapsed divided by the total progress through
+        # self.length.
+        if self.pos:
+            step = (time.time() - self.start) / self.pos
+        else:
+            step = time.time() - self.start
+
+        self.avg = self.avg[-6:] + [step]
 
         self.eta_known = self.length_known