pythongh-58032: Deprecate the argparse.FileType type converter (pythonGH-124664)

Author: serhiy-storchaka

Doc/deprecations/pending-removal-in-future.rst

@@ -4,16 +4,6 @@ Pending removal in future versions
 The following APIs will be removed in the future,
 although there is currently no date scheduled for their removal.
 
-* :mod:`argparse`:
-
-  * Nesting argument groups and nesting mutually exclusive
-    groups are deprecated.
-  * Passing the undocumented keyword argument *prefix_chars* to
-    :meth:`~argparse.ArgumentParser.add_argument_group` is now
-    deprecated.
-
-* :mod:`array`'s ``'u'`` format code (:gh:`57281`)
-
 * :mod:`builtins`:
 
   * ``bool(NotImplemented)``.
@@ -43,6 +33,17 @@ although there is currently no date scheduled for their removal.
     as a single positional argument.
     (Contributed by Serhiy Storchaka in :gh:`109218`.)
 
+* :mod:`argparse`:
+
+  * Nesting argument groups and nesting mutually exclusive
+    groups are deprecated.
+  * Passing the undocumented keyword argument *prefix_chars* to
+    :meth:`~argparse.ArgumentParser.add_argument_group` is now
+    deprecated.
+  * The :class:`argparse.FileType` type converter is deprecated.
+
+* :mod:`array`'s ``'u'`` format code (:gh:`57281`)
+
 * :mod:`calendar`: ``calendar.January`` and ``calendar.February`` constants are
   deprecated and replaced by :data:`calendar.JANUARY` and
   :data:`calendar.FEBRUARY`.

Doc/library/argparse.rst

@@ -865,16 +865,14 @@ See also :ref:`specifying-ambiguous-arguments`. The supported values are:
   output files::
 
      >>> parser = argparse.ArgumentParser()
-     >>> parser.add_argument('infile', nargs='?', type=argparse.FileType('r'),
-     ...                     default=sys.stdin)
-     >>> parser.add_argument('outfile', nargs='?', type=argparse.FileType('w'),
-     ...                     default=sys.stdout)
+     >>> parser.add_argument('infile', nargs='?')
+     >>> parser.add_argument('outfile', nargs='?')
      >>> parser.parse_args(['input.txt', 'output.txt'])
-     Namespace(infile=<_io.TextIOWrapper name='input.txt' encoding='UTF-8'>,
-               outfile=<_io.TextIOWrapper name='output.txt' encoding='UTF-8'>)
+     Namespace(infile='input.txt', outfile='output.txt')
+     >>> parser.parse_args(['input.txt'])
+     Namespace(infile='input.txt', outfile=None)
      >>> parser.parse_args([])
-     Namespace(infile=<_io.TextIOWrapper name='<stdin>' encoding='UTF-8'>,
-               outfile=<_io.TextIOWrapper name='<stdout>' encoding='UTF-8'>)
+     Namespace(infile=None, outfile=None)
 
 .. index:: single: * (asterisk); in argparse module
 
@@ -1033,7 +1031,6 @@ Common built-in types and functions can be used as type converters:
    parser.add_argument('distance', type=float)
    parser.add_argument('street', type=ascii)
    parser.add_argument('code_point', type=ord)
-   parser.add_argument('dest_file', type=argparse.FileType('w', encoding='latin-1'))
    parser.add_argument('datapath', type=pathlib.Path)
 
 User defined functions can be used as well:
@@ -1827,9 +1824,19 @@ FileType objects
       >>> parser.parse_args(['-'])
       Namespace(infile=<_io.TextIOWrapper name='<stdin>' encoding='UTF-8'>)
 
+   .. note::
+
+      If one argument uses *FileType* and then a subsequent argument fails,
+      an error is reported but the file is not automatically closed.
+      This can also clobber the output files.
+      In this case, it would be better to wait until after the parser has
+      run and then use the :keyword:`with`-statement to manage the files.
+
    .. versionchanged:: 3.4
       Added the *encodings* and *errors* parameters.
 
+   .. deprecated:: 3.14
+
 
 Argument groups
 ^^^^^^^^^^^^^^^

Doc/whatsnew/3.14.rst

@@ -464,6 +464,12 @@ Deprecated
   as a single positional argument.
   (Contributed by Serhiy Storchaka in :gh:`109218`.)
 
+* :mod:`argparse`:
+  Deprecated the :class:`argparse.FileType` type converter.
+  Anything with resource management should be done downstream after the
+  arguments are parsed.
+  (Contributed by Serhiy Storchaka in :gh:`58032`.)
+
 * :mod:`multiprocessing` and :mod:`concurrent.futures`:
   The default start method (see :ref:`multiprocessing-start-methods`) changed
   away from *fork* to *forkserver* on platforms where it was not already

Lib/argparse.py

@@ -18,11 +18,12 @@
         'integers', metavar='int', nargs='+', type=int,
         help='an integer to be summed')
     parser.add_argument(
-        '--log', default=sys.stdout, type=argparse.FileType('w'),
+        '--log',
         help='the file where the sum should be written')
     args = parser.parse_args()
-    args.log.write('%s' % sum(args.integers))
-    args.log.close()
+    with (open(args.log, 'w') if args.log is not None
+          else contextlib.nullcontext(sys.stdout)) as log:
+        log.write('%s' % sum(args.integers))
 
 The module contains the following public classes:
 
@@ -39,7 +40,8 @@
 
     - FileType -- A factory for defining types of files to be created. As the
         example above shows, instances of FileType are typically passed as
-        the type= argument of add_argument() calls.
+        the type= argument of add_argument() calls. Deprecated since
+        Python 3.14.
 
     - Action -- The base class for parser actions. Typically actions are
         selected by passing strings like 'store_true' or 'append_const' to
@@ -1252,7 +1254,7 @@ def __call__(self, parser, namespace, values, option_string=None):
 # ==============
 
 class FileType(object):
-    """Factory for creating file object types
+    """Deprecated factory for creating file object types
 
     Instances of FileType are typically passed as type= arguments to the
     ArgumentParser add_argument() method.
@@ -1269,6 +1271,12 @@ class FileType(object):
     """
 
     def __init__(self, mode='r', bufsize=-1, encoding=None, errors=None):
+        import warnings
+        warnings.warn(
+            "FileType is deprecated. Simply open files after parsing arguments.",
+            category=PendingDeprecationWarning,
+            stacklevel=2
+        )
         self._mode = mode
         self._bufsize = bufsize
         self._encoding = encoding

Lib/test/test_argparse.py

@@ -1773,27 +1773,43 @@ def convert_arg_line_to_args(self, arg_line):
 # Type conversion tests
 # =====================
 
+def FileType(*args, **kwargs):
+    with warnings.catch_warnings():
+        warnings.filterwarnings('ignore', 'FileType is deprecated',
+                                PendingDeprecationWarning, __name__)
+        return argparse.FileType(*args, **kwargs)
+
+
+class TestFileTypeDeprecation(TestCase):
+
+    def test(self):
+        with self.assertWarns(PendingDeprecationWarning) as cm:
+            argparse.FileType()
+        self.assertIn('FileType is deprecated', str(cm.warning))
+        self.assertEqual(cm.filename, __file__)
+
+
 class TestFileTypeRepr(TestCase):
 
     def test_r(self):
-        type = argparse.FileType('r')
+        type = FileType('r')
         self.assertEqual("FileType('r')", repr(type))
 
     def test_wb_1(self):
-        type = argparse.FileType('wb', 1)
+        type = FileType('wb', 1)
         self.assertEqual("FileType('wb', 1)", repr(type))
 
     def test_r_latin(self):
-        type = argparse.FileType('r', encoding='latin_1')
+        type = FileType('r', encoding='latin_1')
         self.assertEqual("FileType('r', encoding='latin_1')", repr(type))
 
     def test_w_big5_ignore(self):
-        type = argparse.FileType('w', encoding='big5', errors='ignore')
+        type = FileType('w', encoding='big5', errors='ignore')
         self.assertEqual("FileType('w', encoding='big5', errors='ignore')",
                          repr(type))
 
     def test_r_1_replace(self):
-        type = argparse.FileType('r', 1, errors='replace')
+        type = FileType('r', 1, errors='replace')
         self.assertEqual("FileType('r', 1, errors='replace')", repr(type))
 
 
@@ -1847,7 +1863,6 @@ def __eq__(self, other):
             text = text.decode('ascii')
         return self.name == other.name == text
 
-
 class TestFileTypeR(TempDirMixin, ParserTestCase):
     """Test the FileType option/argument type for reading files"""
 
@@ -1860,8 +1875,8 @@ def setUp(self):
         self.create_readonly_file('readonly')
 
     argument_signatures = [
-        Sig('-x', type=argparse.FileType()),
-        Sig('spam', type=argparse.FileType('r')),
+        Sig('-x', type=FileType()),
+        Sig('spam', type=FileType('r')),
     ]
     failures = ['-x', '', 'non-existent-file.txt']
     successes = [
@@ -1881,7 +1896,7 @@ def setUp(self):
         file.close()
 
     argument_signatures = [
-        Sig('-c', type=argparse.FileType('r'), default='no-file.txt'),
+        Sig('-c', type=FileType('r'), default='no-file.txt'),
     ]
     # should provoke no such file error
     failures = ['']
@@ -1900,8 +1915,8 @@ def setUp(self):
                 file.write(file_name)
 
     argument_signatures = [
-        Sig('-x', type=argparse.FileType('rb')),
-        Sig('spam', type=argparse.FileType('rb')),
+        Sig('-x', type=FileType('rb')),
+        Sig('spam', type=FileType('rb')),
     ]
     failures = ['-x', '']
     successes = [
@@ -1939,8 +1954,8 @@ def setUp(self):
         self.create_writable_file('writable')
 
     argument_signatures = [
-        Sig('-x', type=argparse.FileType('w')),
-        Sig('spam', type=argparse.FileType('w')),
+        Sig('-x', type=FileType('w')),
+        Sig('spam', type=FileType('w')),
     ]
     failures = ['-x', '', 'readonly']
     successes = [
@@ -1962,8 +1977,8 @@ def setUp(self):
         self.create_writable_file('writable')
 
     argument_signatures = [
-        Sig('-x', type=argparse.FileType('x')),
-        Sig('spam', type=argparse.FileType('x')),
+        Sig('-x', type=FileType('x')),
+        Sig('spam', type=FileType('x')),
     ]
     failures = ['-x', '', 'readonly', 'writable']
     successes = [
@@ -1977,8 +1992,8 @@ class TestFileTypeWB(TempDirMixin, ParserTestCase):
     """Test the FileType option/argument type for writing binary files"""
 
     argument_signatures = [
-        Sig('-x', type=argparse.FileType('wb')),
-        Sig('spam', type=argparse.FileType('wb')),
+        Sig('-x', type=FileType('wb')),
+        Sig('spam', type=FileType('wb')),
     ]
     failures = ['-x', '']
     successes = [
@@ -1994,8 +2009,8 @@ class TestFileTypeXB(TestFileTypeX):
     "Test the FileType option/argument type for writing new binary files only"
 
     argument_signatures = [
-        Sig('-x', type=argparse.FileType('xb')),
-        Sig('spam', type=argparse.FileType('xb')),
+        Sig('-x', type=FileType('xb')),
+        Sig('spam', type=FileType('xb')),
     ]
     successes = [
         ('-x foo bar', NS(x=WFile('foo'), spam=WFile('bar'))),
@@ -2007,7 +2022,7 @@ class TestFileTypeOpenArgs(TestCase):
     """Test that open (the builtin) is correctly called"""
 
     def test_open_args(self):
-        FT = argparse.FileType
+        FT = FileType
         cases = [
             (FT('rb'), ('rb', -1, None, None)),
             (FT('w', 1), ('w', 1, None, None)),
@@ -2022,7 +2037,7 @@ def test_open_args(self):
 
     def test_invalid_file_type(self):
         with self.assertRaises(ValueError):
-            argparse.FileType('b')('-test')
+            FileType('b')('-test')
 
 
 class TestFileTypeMissingInitialization(TestCase):

Misc/NEWS.d/next/Library/2024-09-27-13-10-17.gh-issue-58032.0aNAQ0.rst

@@ -0,0 +1 @@
+Deprecate the :class:`argparse.FileType` type converter.