From 93951a4a08d14aa9deca1b1d9e4dc1afd2684534 Mon Sep 17 00:00:00 2001
From: Maxwell Bernstein <emacs@fb.com>
Date: Wed, 18 Mar 2020 16:47:24 -0700
Subject: [PATCH 1/2] bpo-39985: Make string.Formatter with empty field name
 default to 0

This causes string.Formatter to behave like str.format in cases like
`"[0]".format((1, 2, 3))`, where `[0]` implicitly refers to the first
argument to `str.format`.
---
 Lib/string.py           | 5 +++++
 Lib/test/test_string.py | 1 +
 2 files changed, 6 insertions(+)

diff --git a/Lib/string.py b/Lib/string.py
index 489777b10c25df7..6bad050eef5ca34 100644
--- a/Lib/string.py
+++ b/Lib/string.py
@@ -222,8 +222,13 @@ def _vformat(self, format_string, args, kwargs, used_args, recursion_depth,
 
     def get_value(self, key, args, kwargs):
         if isinstance(key, int):
+            # "1234[x]"
             return args[key]
+        elif key == "":
+            # "[x]"
+            return args[0]
         else:
+            # "abcd[x]"
             return kwargs[key]
 
 
diff --git a/Lib/test/test_string.py b/Lib/test/test_string.py
index 0be28fdb609eaee..bca5d165ab83a74 100644
--- a/Lib/test/test_string.py
+++ b/Lib/test/test_string.py
@@ -96,6 +96,7 @@ def test_index_lookup(self):
         fmt = string.Formatter()
         lookup = ["eggs", "and", "spam"]
         self.assertEqual(fmt.format("{0[2]}{0[0]}", lookup), 'spameggs')
+        self.assertEqual(fmt.format("{[2]}{1[0]}", lookup, (1, 2, 3)), 'spam1')
         with self.assertRaises(IndexError):
             fmt.format("{0[2]}{0[0]}", [])
         with self.assertRaises(KeyError):

From a6bc0ef6cec9419620c26373688a02f12953d13b Mon Sep 17 00:00:00 2001
From: "blurb-it[bot]" <43283697+blurb-it[bot]@users.noreply.github.com>
Date: Thu, 19 Mar 2020 00:20:32 +0000
Subject: [PATCH 2/2] =?UTF-8?q?=F0=9F=93=9C=F0=9F=A4=96=20Added=20by=20blu?=
 =?UTF-8?q?rb=5Fit.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../NEWS.d/next/Library/2020-03-19-00-20-28.bpo-39985.4ki_Ed.rst | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-03-19-00-20-28.bpo-39985.4ki_Ed.rst

diff --git a/Misc/NEWS.d/next/Library/2020-03-19-00-20-28.bpo-39985.4ki_Ed.rst b/Misc/NEWS.d/next/Library/2020-03-19-00-20-28.bpo-39985.4ki_Ed.rst
new file mode 100644
index 000000000000000..951e76acceaaef8
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-03-19-00-20-28.bpo-39985.4ki_Ed.rst
@@ -0,0 +1 @@
+Make string.Formatter behave like str.format with anonymous subscripts.
\ No newline at end of file