From 8af0c666ad99ba27ede4352bc8714c333e9d8d84 Mon Sep 17 00:00:00 2001
From: "Eric V. Smith" <eric@trueblade.com>
Date: Thu, 27 Aug 2015 10:20:59 -0400
Subject: [PATCH] Added a note that the str.format() parser is not suitable for
 use when implementing f-strings.

---
 pep-0498.txt | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pep-0498.txt b/pep-0498.txt
index d58f7f01f..85b028f80 100644
--- a/pep-0498.txt
+++ b/pep-0498.txt
@@ -470,6 +470,15 @@ use variables as index values::
   >>> f'a={d[a]}'
   'a=20'
 
+Furthermore, the limited expressions that str.format() understands
+need not be valid Python expressions. For example::
+
+  >>> '{i[";]}'.format(i={'";':4})
+  '4'
+
+For this reason, the str.format() "expression parser" is not suitable
+for use when implementing f-strings.
+
 See [#]_ for a further discussion. It was this observation that led to
 full Python expressions being supported in f-strings.