ipython · ivanov · Jun 24, 2021 · Jun 24, 2021 · Jun 24, 2021 · Jun 25, 2021
diff --git a/IPython/core/magic_arguments.py b/IPython/core/magic_arguments.py
@@ -132,7 +132,7 @@ def error(self, message):
     def parse_argstring(self, argstring):
         """ Split a string into an argument list and parse that argument list.
         """
-        argv = arg_split(argstring)
+        argv = arg_split(argstring, posix=True, strict=False)
         return self.parse_args(argv)
 
 

diff --git a/IPython/core/magics/osm.py b/IPython/core/magics/osm.py
@@ -842,10 +842,7 @@ def writefile(self, line, cell):
         The file will be overwritten unless the -a (--append) flag is specified.
         """
         args = magic_arguments.parse_argstring(self.writefile, line)
-        if re.match(r'^(\'.*\')|(".*")$', args.filename):
-            filename = os.path.expanduser(args.filename[1:-1])
-        else:
-            filename = os.path.expanduser(args.filename)
+        filename = os.path.expanduser(args.filename)
 
         if os.path.exists(filename):
             if args.append:

diff --git a/IPython/core/tests/test_magic.py b/IPython/core/tests/test_magic.py
@@ -860,11 +860,17 @@ def test_file_single_quote():
     """Basic %%writefile with embedded single quotes"""
     ip = get_ipython()
     with TemporaryDirectory() as td:
-        fname = os.path.join(td, '\'file1\'')
-        ip.run_cell_magic("writefile", fname, u'\n'.join([
-            'line1',
-            'line2',
-        ]))
+        fname = os.path.join(td, "'file1'")
+        ip.run_cell_magic(
+            "writefile",
+            '"%s"' % fname,
+            u"\n".join(
+                [
+                    "line1",
+                    "line2",
+                ]
+            ),
+        )
         s = Path(fname).read_text()
         nt.assert_in('line1\n', s)
         nt.assert_in('line2', s)
@@ -875,10 +881,16 @@ def test_file_double_quote():
     ip = get_ipython()
     with TemporaryDirectory() as td:
         fname = os.path.join(td, '"file1"')
-        ip.run_cell_magic("writefile", fname, u'\n'.join([
-            'line1',
-            'line2',
-        ]))
+        ip.run_cell_magic(
+            "writefile",
+            "'%s'" % fname,
+            u"\n".join(
+                [
+                    "line1",
+                    "line2",
+                ]
+            ),
+        )
         s = Path(fname).read_text()
         nt.assert_in('line1\n', s)
         nt.assert_in('line2', s)

diff --git a/IPython/core/tests/test_magic_arguments.py b/IPython/core/tests/test_magic_arguments.py
@@ -116,3 +116,21 @@ def test_magic_arguments():
     assert_equal(real_name(foo), 'foo')
     assert_equal(foo(None, ''), argparse.Namespace(foo=None))
     assert hasattr(foo, 'has_arguments')
+
+
+@magic_arguments()
+@argument("filepath", type=str, nargs=1, help="An argument with possible spaces")
+def magic_one_arg(args):
+    return parse_argstring(magic_one_arg, args)
+
+
+def test_spaces_and_quotes():
+    "Test for GH-12729"
+    assert_equal(
+        parse_argstring(magic_one_arg, '"this is one arg"'),
+        argparse.Namespace(filepath=["this is one arg"]),
+    )
+    assert_equal(
+        parse_argstring(magic_one_arg, "this\ is\ also\ one\ arg"),
+        argparse.Namespace(filepath=["this is also one arg"]),
+    )
diff --git a/docs/source/whatsnew/pr/incompat-quotes-magic-argument.rst b/docs/source/whatsnew/pr/incompat-quotes-magic-argument.rst
@@ -0,0 +1,35 @@
+Incompatible change to the way magics handle spaces and quotes
+--------------------------------------------------------------
+
+Magics that previously split on whitespace for arguments now preserve
+backslash-escaped whitespace and whitespace inside of quotes. This allows for
+filenames that have spaces to be treated the same as files without spaces.
+However, this change is backwards incompatible with previous behavior of
+preserving un-escaped quotes in the `writefile` magic, for example.
+
+So if you previously had code like
+
+`%%writefile File"With"Quotes`
+
+You must now write
+
+`%%writefile 'File"With"Quotes`
+
+or 
+
+`%%writefile File\"With\"Quotes'`
+
+
+It was also the case that, due to some special-casing, surrounding quotes for
+a filename containing spaces for writefile did work (`%%writefile "File with
+spaces"`), the escaping of the same file name did not (`%%writefile File\
+with\ spaces` would fail with "UsageError: unrecognized arguments: with\
+spaces"). Now, both cases work the same.
+
+The underlying change was to have
+:meth:`~IPython.core.magics_arguments.parse_argstring` pass `posix=True` and
+`strict=False` when calling `arg_split`.
+
+This change fixes :ghissue:`12729`, for full details, please see
+:ghpull:`13027`
+