newforms-admin: Merged from trunk up to [7814].

git-svn-id: http://code.djangoproject.com/svn/django/branches/newforms-admin@7815 bcc190cf-cafb-0310-a4f2-bffc1f526a37

1 files changed, 59 insertions, 0 deletions

diff --git a/django/core/files/move.py b/django/core/files/move.py
new file mode 100644
index 0000000000..66873d450c
--- /dev/null
+++ b/django/core/files/move.py
@@ -0,0 +1,59 @@
+"""
+Move a file in the safest way possible::
+
+    >>> from django.core.files.move import file_move_save
+    >>> file_move_save("/tmp/old_file", "/tmp/new_file")
+"""
+
+import os
+from django.core.files import locks
+
+__all__ = ['file_move_safe']
+
+try:
+    import shutil
+    file_move = shutil.move
+except ImportError:
+    file_move = os.rename
+
+def file_move_safe(old_file_name, new_file_name, chunk_size = 1024*64, allow_overwrite=False):
+    """
+    Moves a file from one location to another in the safest way possible.
+
+    First, try using ``shutils.move``, which is OS-dependent but doesn't break
+    if moving across filesystems. Then, try ``os.rename``, which will break
+    across filesystems. Finally, streams manually from one file to another in
+    pure Python.
+
+    If the destination file exists and ``allow_overwrite`` is ``False``, this
+    function will throw an ``IOError``.
+    """
+
+    # There's no reason to move if we don't have to.
+    if old_file_name == new_file_name:
+        return
+
+    if not allow_overwrite and os.path.exists(new_file_name):
+        raise IOError("Cannot overwrite existing file '%s'." % new_file_name)
+
+    try:
+        file_move(old_file_name, new_file_name)
+        return
+    except OSError:
+        # This will happen with os.rename if moving to another filesystem
+        pass
+
+    # If the built-in didn't work, do it the hard way.
+    new_file = open(new_file_name, 'wb')
+    locks.lock(new_file, locks.LOCK_EX)
+    old_file = open(old_file_name, 'rb')
+    current_chunk = None
+
+    while current_chunk != '':
+        current_chunk = old_file.read(chunk_size)
+        new_file.write(current_chunk)
+
+    new_file.close()
+    old_file.close()
+
+    os.remove(old_file_name)