#1492704: Make shutil.copyfile() raise a distinct SameFileError

Patch by Atsuo Ishimoto.

Doc/library/shutil.rst

@@ -52,7 +52,7 @@ Directory and files operations
    Copy the contents (no metadata) of the file named *src* to a file named
    *dst* and return *dst*.  *dst* must be the complete target file name; look at
    :func:`shutil.copy` for a copy that accepts a target directory path.  If
-   *src* and *dst* are the same files, :exc:`Error` is raised.
+   *src* and *dst* are the same files, :exc:`SameFileError` is raised.
 
    The destination location must be writable; otherwise,  an :exc:`OSError` exception
    will be raised. If *dst* already exists, it will be replaced.   Special files
@@ -67,6 +67,16 @@ Directory and files operations
       :exc:`IOError` used to be raised instead of :exc:`OSError`.
       Added *follow_symlinks* argument.
       Now returns *dst*.
+      Raise :exc:`SameFileError` instead of :exc:`Error`.
+
+
+.. exception:: SameFileError
+
+   This exception is raised if source and destination in :func:`copyfile`
+   are the same file.
+
+   .. versionadded:: 3.3
+
 
 .. function:: copymode(src, dst, *, follow_symlinks=True)
 

Lib/shutil.py

@@ -42,6 +42,9 @@ __all__ = ["copyfileobj", "copyfile", "copymode", "copystat", "copy", "copy2",
 class Error(EnvironmentError):
     pass
 
+class SameFileError(Error):
+    """Raised when source and destination are the same file."""
+
 class SpecialFileError(EnvironmentError):
     """Raised when trying to do a kind of operation (e.g. copying) which is
     not supported on a special file (e.g. a named pipe)"""
@@ -90,7 +93,7 @@ def copyfile(src, dst, *, follow_symlinks=True):
 
     """
     if _samefile(src, dst):
-        raise Error("`%s` and `%s` are the same file" % (src, dst))
+        raise SameFileError("{!r} and {!r} are the same file".format(src, dst))
 
     for fn in [src, dst]:
         try:
@@ -215,6 +218,9 @@ def copy(src, dst, *, follow_symlinks=True):
     If follow_symlinks is false, symlinks won't be followed. This
     resembles GNU's "cp -P src dst".
 
+    If source and destination are the same file, a SameFileError will be
+    raised.
+
     """
     if os.path.isdir(dst):
         dst = os.path.join(dst, os.path.basename(src))

Lib/test/test_shutil.py

@@ -18,7 +18,8 @@ from shutil import (_make_tarball, _make_zipfile, make_archive,
                     register_archive_format, unregister_archive_format,
                     get_archive_formats, Error, unpack_archive,
                     register_unpack_format, RegistryError,
-                    unregister_unpack_format, get_unpack_formats)
+                    unregister_unpack_format, get_unpack_formats,
+                    SameFileError)
 import tarfile
 import warnings
 
@@ -688,7 +689,7 @@ class TestShutil(unittest.TestCase):
             with open(src, 'w') as f:
                 f.write('cheddar')
             os.link(src, dst)
-            self.assertRaises(shutil.Error, shutil.copyfile, src, dst)
+            self.assertRaises(shutil.SameFileError, shutil.copyfile, src, dst)
             with open(src, 'r') as f:
                 self.assertEqual(f.read(), 'cheddar')
             os.remove(dst)
@@ -708,7 +709,7 @@ class TestShutil(unittest.TestCase):
             # to TESTFN/TESTFN/cheese, while it should point at
             # TESTFN/cheese.
             os.symlink('cheese', dst)
-            self.assertRaises(shutil.Error, shutil.copyfile, src, dst)
+            self.assertRaises(shutil.SameFileError, shutil.copyfile, src, dst)
             with open(src, 'r') as f:
                 self.assertEqual(f.read(), 'cheddar')
             os.remove(dst)
@@ -1215,6 +1216,14 @@ class TestShutil(unittest.TestCase):
         self.assertTrue(os.path.exists(rv))
         self.assertEqual(read_file(src_file), read_file(dst_file))
 
+    def test_copyfile_same_file(self):
+        # copyfile() should raise SameFileError if the source and destination
+        # are the same.
+        src_dir = self.mkdtemp()
+        src_file = os.path.join(src_dir, 'foo')
+        write_file(src_file, 'foo')
+        self.assertRaises(SameFileError, shutil.copyfile, src_file, src_file)
+
     def test_copytree_return_value(self):
         # copytree returns its destination path.
         src_dir = self.mkdtemp()

Misc/NEWS

@@ -44,6 +44,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #1492704: shutil.copyfile() raises a distinct SameFileError now if
+  source and destination are the same file. Patch by Atsuo Ishimoto.
+
 - Issue #15397: inspect.getmodulename() is now based directly on importlib
   via a new importlib.machinery.all_suffixes() API.