From 6d3583dc6ff0dfffad6e13218f32a1d67b67119f Mon Sep 17 00:00:00 2001
From: hauntsaninja <>
Date: Sat, 1 Aug 2020 19:40:04 -0700
Subject: [PATCH] messages: clarify bytes repr errors

Resolves #9236
---
 mypy/checkstrformat.py | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mypy/checkstrformat.py b/mypy/checkstrformat.py
index f3081a2fa491..b9a2a4099e52 100644
--- a/mypy/checkstrformat.py
+++ b/mypy/checkstrformat.py
@@ -384,9 +384,10 @@ def perform_special_format_checks(self, spec: ConversionSpecifier, call: CallExp
             if self.chk.options.python_version >= (3, 0):
                 if (has_type_component(actual_type, 'builtins.bytes') and
                         not custom_special_method(actual_type, '__str__')):
-                    self.msg.fail("On Python 3 '{}'.format(b'abc') produces \"b'abc'\";"
-                                  " use !r if this is a desired behavior", call,
-                                  code=codes.STR_BYTES_PY3)
+                    self.msg.fail(
+                        "On Python 3 '{}'.format(b'abc') produces \"b'abc'\", not 'abc'; "
+                        "use '{!r}'.format(b'abc') if this is desired behavior",
+                        call, code=codes.STR_BYTES_PY3)
         if spec.flags:
             numeric_types = UnionType([self.named_type('builtins.int'),
                                        self.named_type('builtins.float')])
@@ -843,9 +844,10 @@ def check_s_special_cases(self, expr: FormatStringExpr, typ: Type, context: Cont
             # Couple special cases for string formatting.
             if self.chk.options.python_version >= (3, 0):
                 if has_type_component(typ, 'builtins.bytes'):
-                    self.msg.fail("On Python 3 '%s' % b'abc' produces \"b'abc'\";"
-                                  " use %r if this is a desired behavior", context,
-                                  code=codes.STR_BYTES_PY3)
+                    self.msg.fail(
+                        "On Python 3 '%s' % b'abc' produces \"b'abc'\", not 'abc'; "
+                        "use '%r' % b'abc' if this is desired behavior",
+                        context, code=codes.STR_BYTES_PY3)
             if self.chk.options.python_version < (3, 0):
                 if has_type_component(typ, 'builtins.unicode'):
                     self.unicode_upcast = True