From aaf392c6efd32a6025c26847d02f952dcf700ba7 Mon Sep 17 00:00:00 2001
From: Abdu Ahmed <iamabduahmed@gmail.com>
Date: Sun, 24 May 2026 11:47:23 +0300
Subject: [PATCH] Fix --sort-reexports crash with non-seekable streams (e.g.
 stdin)

When --sort-reexports was used with stdin, isort crashed with
io.UnsupportedOperation because core.process() called seek() on
stdout, which is not seekable.

Fix: in api.sort_stream(), if sort_reexports is enabled and the
output stream is not seekable, swap it for an internal StringIO
buffer before passing to core.process().

Fixes #2393
---
 isort/api.py                   |  2 ++
 tests/unit/test_regressions.py | 24 ++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/isort/api.py b/isort/api.py
index abf8bdb1..43dec051 100644
--- a/isort/api.py
+++ b/isort/api.py
@@ -203,6 +203,8 @@ def sort_stream(
         if not output_stream.readable():
             _internal_output = StringIO()
 
+    if config.sort_reexports and not _internal_output.seekable():
+        _internal_output = StringIO()
     try:
         changed = core.process(
             input_stream,
diff --git a/tests/unit/test_regressions.py b/tests/unit/test_regressions.py
index bd0e538d..34920867 100644
--- a/tests/unit/test_regressions.py
+++ b/tests/unit/test_regressions.py
@@ -1985,3 +1985,27 @@ def test_comment_on_opening_line_of_aliased_import_does_not_move():
         isort.code(short_line, profile="black")
         == "from mod import attr as alias  # type: ignore[attr-defined]  # My comment\n"
     )
+
+def test_sort_reexports_with_non_seekable_stream_issue_2393():
+    """Ensure --sort-reexports does not crash when output stream is non-seekable (e.g. stdin).
+    See: https://github.com/PyCQA/isort/issues/2393
+    """
+    import sys
+    from io import StringIO
+
+    code = "from test import B, A\n__all__ = ['B', 'A']\n"
+    input_stream = StringIO(code)
+    isort.api.sort_stream(
+        input_stream=input_stream,
+        output_stream=sys.stdout,
+        sort_reexports=True,
+    )
+    input_stream = StringIO(code)
+    output_stream = StringIO()
+    isort.api.sort_stream(
+        input_stream=input_stream,
+        output_stream=output_stream,
+        sort_reexports=True,
+    )
+    output_stream.seek(0)
+    assert "import A, B" in output_stream.read()
\ No newline at end of file