From 109fc2792a490ee5cd8a423e17d415fbdedec5c8 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Batuhan=20Ta=C5=9Fkaya?=
 <47358913+isidentical@users.noreply.github.com>
Date: Mon, 9 Dec 2019 07:36:27 +0300
Subject: bpo-38673: dont switch to ps2 if the line starts with comment or
 whitespace (GH-17421)

https://bugs.python.org/issue38673
---
 .../next/Core and Builtins/2019-12-01-00-17-44.bpo-38673.K_Tze-.rst | 1 +
 Parser/tokenizer.c                                                  | 6 ++++++
 2 files changed, 7 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2019-12-01-00-17-44.bpo-38673.K_Tze-.rst

diff --git a/Misc/NEWS.d/next/Core and Builtins/2019-12-01-00-17-44.bpo-38673.K_Tze-.rst b/Misc/NEWS.d/next/Core and Builtins/2019-12-01-00-17-44.bpo-38673.K_Tze-.rst
new file mode 100644
index 0000000..8f8cf88
--- /dev/null
+++ b/Misc/NEWS.d/next/Core and Builtins/2019-12-01-00-17-44.bpo-38673.K_Tze-.rst	
@@ -0,0 +1 @@
+In REPL mode, don't switch to PS2 if the line starts with comment or whitespace. Based on work by Batuhan Taşkaya.
diff --git a/Parser/tokenizer.c b/Parser/tokenizer.c
index 5763e47..f84093d 100644
--- a/Parser/tokenizer.c
+++ b/Parser/tokenizer.c
@@ -1148,6 +1148,12 @@ tok_get(struct tok_state *tok, char **p_start, char **p_end)
             if (col == 0 && c == '\n' && tok->prompt != NULL) {
                 blankline = 0; /* Let it through */
             }
+            else if (tok->prompt != NULL && tok->lineno == 1) {
+                /* In interactive mode, if the first line contains
+                   only spaces and/or a comment, let it through. */
+                blankline = 0;
+                col = altcol = 0;
+            }
             else {
                 blankline = 1; /* Ignore completely */
             }
-- 
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