From 59de879c057b520b8b5b0ba414055bff9e6416af Mon Sep 17 00:00:00 2001
From: Vincent Gao <gaobing1230@gmail.com>
Date: Wed, 24 Jun 2026 23:27:46 +0200
Subject: [PATCH] Fix get_matrix() aliasing border rows when border > 1
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`[[False] * width] * self.border` creates *border* references to the
same inner list object.  When border > 1 this means all top (or all
bottom) border rows in the returned matrix share a single backing list,
so mutating any one of them silently corrupts the rest.

Replace the list-multiplication with list comprehensions to give every
border row its own independent list.

Reproducer (raises AssertionError before this fix):

    qr = QRCode(border=4)
    qr.add_data("1")
    m = qr.get_matrix()
    assert m[0] is not m[1]   # was the *same* list – False without fix

Adds a regression test that verifies row identity and all-False content
for each border row when border=4.
---
 qrcode/main.py              |  4 ++--
 qrcode/tests/test_qrcode.py | 29 +++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/qrcode/main.py b/qrcode/main.py
index 593c581b..929ef120 100644
--- a/qrcode/main.py
+++ b/qrcode/main.py
@@ -523,11 +523,11 @@ def get_matrix(self):
             return self.modules
 
         width = len(self.modules) + self.border * 2
-        code = [[False] * width] * self.border
+        code = [[False] * width for _ in range(self.border)]
         x_border = [False] * self.border
         for module in self.modules:
             code.append(x_border + cast("list[bool]", module) + x_border)
-        code += [[False] * width] * self.border
+        code += [[False] * width for _ in range(self.border)]
 
         return code
 
diff --git a/qrcode/tests/test_qrcode.py b/qrcode/tests/test_qrcode.py
index a98f8724..285ee21f 100644
--- a/qrcode/tests/test_qrcode.py
+++ b/qrcode/tests/test_qrcode.py
@@ -43,8 +43,7 @@ def test_glog_zero_binary_data_at_capacity():
     # Version 5 + Q = 60 bytes capacity, data padded with trailing null bytes
     data = (
         b"\x00\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x16"
-        b"Hello from kakaworld!!"
-        + b"\x00" * 26
+        b"Hello from kakaworld!!" + b"\x00" * 26
     )
     assert len(data) == 60
     qr = qrcode.QRCode(version=5, error_correction=qrcode.constants.ERROR_CORRECT_Q)
@@ -303,6 +302,32 @@ def test_get_matrix_border():
     assert matrix == qr.modules
 
 
+def test_get_matrix_border_rows_not_aliased():
+    # With border > 1, each border row must be a distinct list object so that
+    # mutating one row does not corrupt the others.
+    qr = qrcode.QRCode(border=4)
+    qr.add_data("1")
+    matrix = qr.get_matrix()
+    border = qr.border
+    top_rows = matrix[:border]
+    bottom_rows = matrix[-border:]
+    # Every pair of top border rows must be distinct objects.
+    for i in range(border):
+        for j in range(i + 1, border):
+            assert top_rows[i] is not top_rows[j], (
+                f"Top border rows {i} and {j} are the same object (aliased)"
+            )
+    # Every pair of bottom border rows must be distinct objects.
+    for i in range(border):
+        for j in range(i + 1, border):
+            assert bottom_rows[i] is not bottom_rows[j], (
+                f"Bottom border rows {i} and {j} are the same object (aliased)"
+            )
+    # All border rows must contain only False values.
+    for row in top_rows + bottom_rows:
+        assert row == [False] * len(row)
+
+
 def test_negative_size_at_construction():
     with pytest.raises(ValueError):
         qrcode.QRCode(box_size=-1)