From 185903de12de8837bf0dc0008a16e5e56c66a019 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Batuhan=20Ta=C5=9Fkaya?=
 <47358913+isidentical@users.noreply.github.com>
Date: Sun, 1 Mar 2020 23:07:22 +0300
Subject: bpo-39520: Fix un-parsing of ext slices with no dimensions (GH-18304)

---
 Lib/test/test_future.py                                              | 5 +++++
 .../next/Core and Builtins/2020-02-02-00-12-07.bpo-39520.uicBq6.rst  | 2 ++
 Python/ast_unparse.c                                                 | 1 +
 3 files changed, 8 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2020-02-02-00-12-07.bpo-39520.uicBq6.rst

diff --git a/Lib/test/test_future.py b/Lib/test/test_future.py
index fd468b5..d83c47e 100644
--- a/Lib/test/test_future.py
+++ b/Lib/test/test_future.py
@@ -256,6 +256,11 @@ class AnnotationsFutureTestCase(unittest.TestCase):
         eq("slice[:-1]")
         eq("slice[1:]")
         eq("slice[::-1]")
+        eq("slice[:,]")
+        eq("slice[1:2,]")
+        eq("slice[1:2:3,]")
+        eq("slice[1:2, 1]")
+        eq("slice[1:2, 2, 3]")
         eq("slice[()]")
         eq("slice[a, b:c, d:e:f]")
         eq("slice[(x for x in a)]")
diff --git a/Misc/NEWS.d/next/Core and Builtins/2020-02-02-00-12-07.bpo-39520.uicBq6.rst b/Misc/NEWS.d/next/Core and Builtins/2020-02-02-00-12-07.bpo-39520.uicBq6.rst
new file mode 100644
index 0000000..dec6765
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2020-02-02-00-12-07.bpo-39520.uicBq6.rst	
@@ -0,0 +1,2 @@
+Fix unparsing of ext slices with no items (``foo[:,]``). Patch by Batuhan
+Taskaya.
diff --git a/Python/ast_unparse.c b/Python/ast_unparse.c
index f376e86..1a7cd23 100644
--- a/Python/ast_unparse.c
+++ b/Python/ast_unparse.c
@@ -746,6 +746,7 @@ append_ast_ext_slice(_PyUnicodeWriter *writer, slice_ty slice)
         APPEND_STR_IF(i > 0, ", ");
         APPEND(slice, (slice_ty)asdl_seq_GET(slice->v.ExtSlice.dims, i));
     }
+    APPEND_STR_IF(dims_count == 1, ",");
     return 0;
 }
 
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