From 75f463a37554177ed13401a08b86f8c3dbbe9091 Mon Sep 17 00:00:00 2001
From: "Eric V. Smith" <eric@trueblade.com>
Date: Fri, 28 Aug 2015 11:16:23 -0400
Subject: [PATCH] Added section on order of evaluation.

---
 pep-0498.txt | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/pep-0498.txt b/pep-0498.txt
index d5ce55ce9..86190ca24 100644
--- a/pep-0498.txt
+++ b/pep-0498.txt
@@ -602,10 +602,24 @@ having 2 expressions::
 
   f'{x:.{width}}'
 
-Expressions with side effects
------------------------------
+Evaluation order of expressions
+-------------------------------
 
-xxx
+The expressions in an f-string are evaluated in left-to-right
+order. This is detectable only if the expressions have side effects::
+
+  >>> def fn(l, incr):
+  ...    result = l[0]
+  ...    l[0] += incr
+  ...    return result
+  ...
+  >>> lst = [0]
+  >>> f'{fn(lst,2)} {fn(lst,3)}'
+  '0 2'
+  >>> f'{fn(lst,2)} {fn(lst,3)}'
+  '5 7'
+  >>> lst
+  [10]
 
 Expressions used multiple times
 -------------------------------