Backport PR #39029: BUG: read_csv does not close file during an error in _make_reader

doc/source/whatsnew/v1.2.1.rst

@@ -40,7 +40,7 @@ Bug fixes
 ~~~~~~~~~
 
 - Bug in :meth:`read_csv` with ``float_precision="high"`` caused segfault or wrong parsing of long exponent strings. This resulted in a regression in some cases as the default for ``float_precision`` was changed in pandas 1.2.0 (:issue:`38753`)
--
+- Bug in :func:`read_csv` not closing an opened file handle when a ``csv.Error`` or ``UnicodeDecodeError`` occurred while initializing (:issue:`39024`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/io/parsers.py

@@ -2288,7 +2288,11 @@ def __init__(self, f: Union[FilePathOrBuffer, List], **kwds):
             self._open_handles(f, kwds)
             assert self.handles is not None
             assert hasattr(self.handles.handle, "readline")
-            self._make_reader(self.handles.handle)
+            try:
+                self._make_reader(self.handles.handle)
+            except (csv.Error, UnicodeDecodeError):
+                self.close()
+                raise
 
         # Get columns in two steps: infer from data, then
         # infer column indices from self.usecols if it is specified.

pandas/tests/io/parser/test_common.py

@@ -8,8 +8,10 @@
 from inspect import signature
 from io import BytesIO, StringIO
 import os
+from pathlib import Path
 import platform
 from urllib.error import URLError
+import warnings
 
 import numpy as np
 import pytest
@@ -2369,3 +2371,22 @@ def test_context_manageri_user_provided(all_parsers, datapath):
                 assert False
         except AssertionError:
             assert not reader._engine.handles.handle.closed
+
+
+@td.check_file_leaks
+def test_open_file(all_parsers):
+    # GH 39024
+    parser = all_parsers
+    if parser.engine == "c":
+        pytest.skip()
+
+    with tm.ensure_clean() as path:
+        file = Path(path)
+        file.write_bytes(b"\xe4\na\n1")
+
+        # should not trigger a ResourceWarning
+        warnings.simplefilter("always", category=ResourceWarning)
+        with warnings.catch_warnings(record=True) as record:
+            with pytest.raises(csv.Error, match="Could not determine delimiter"):
+                parser.read_csv(file, sep=None)
+            assert len(record) == 0, record[0].message