diff --git a/doc/changelog.txt b/doc/changelog.txt
index 6b92765..d157b13 100644
--- a/doc/changelog.txt
+++ b/doc/changelog.txt
@@ -8,6 +8,7 @@
   Closes: SF bug #2977749
 * Added support for the lbzip2 program handling BZIP2 archives.
 * Added support for the plzip program handling LZIP archives.
+* Prevent overwriting the same file with repack.
 
 
 0.15 "Contraband" (released 8.4.2012)
diff --git a/doc/development.txt b/doc/development.txt
new file mode 100644
index 0000000..3f3cd38
--- /dev/null
+++ b/doc/development.txt
@@ -0,0 +1,65 @@
+Development with the patoolib library
+======================================
+
+The patool funtionality can also be used in other Python programs.
+To do this, install the patool program, import the library and
+use one or more of the convenience functions.
+
+import patoolib
+if patoolib.extract("myarchive.zip", verbose=True) == 0:
+    print "Success."
+else:
+    print "Error."
+
+General rules for all convenience functions:
+
+* All convenience function return zero when no error occurred, else
+  an integer unequal zero.
+
+* Error messages are printed on stderr, informative messages
+  are printed on stdout.
+
+* All file arguments are filenames. File objects are not accepted
+  as input.
+
+* Filenames can be relative or absolute.
+
+The convenience functions are:
+
+* ``def extract(archive, verbose=False, outdir=None)``
+  
+  This function extracts the given archive filename to the current
+  working directory or if specified to the given directory name in outdir.
+  If verbose operation is set to True, additional output of the archive
+  program is shown.
+
+* ``def list(archive, verbose=False)``
+  
+  This function lists the contents of the given archive filename
+  on stdout.
+  If verbose operation is set to True, additional output of the archive
+  program is shown.
+
+* ``def test(archive, verbose=False)``
+  
+  This function tests the given archive filename.
+  If verbose operation is set to True, additional output of the archive
+  program is shown.
+
+* ``def create(archive, *filenames, **kwargs)``
+  
+  This function create a new archive. The type of archive is determined
+  by the archive filename extension. The archive must not already
+  exist.
+  The list of filenames to add to the archive must not be empty.
+  If verbose operation is set to True, additional output of the archive
+  program is shown.
+
+* ``def diff(archive1, archive2, verbose=False)``
+  
+  This function 
+
+* ``def repack(archive1, archive2, verbose=False)``
+  
+  This function 
+
diff --git a/patoolib/__init__.py b/patoolib/__init__.py
index cb680cd..424072b 100644
--- a/patoolib/__init__.py
+++ b/patoolib/__init__.py
@@ -398,9 +398,12 @@ def cleanup_outdir (outdir):
 
 def _handle_archive (archive, command, *args, **kwargs):
     """Handle archive command; raising PatoolError on errors."""
-    if command != 'create':
-        # check that archive is a regular file
-        util.check_filename(archive)
+    # check arguments
+    if command == 'create':
+        util.check_archive_filelist(args)
+        util.check_new_filename(archive)
+    else:
+        util.check_existing_filename(archive)
     format, encoding = kwargs.get("format"), kwargs.get("encoding")
     if format is None:
         format, encoding = get_archive_format(archive)
@@ -470,9 +473,14 @@ def rmtree_log_error (func, path, exc):
 
 def _diff_archives (archive1, archive2, **kwargs):
     """Show differences between two archives."""
+    if util.is_same_file(archive1, archive2):
+        msg = "no differences found: archive `%s' and `%s' are the same files"
+        print msg % (archive1, archive2)
+        return 0
     diff = util.find_program("diff")
     if not diff:
-        raise util.PatoolError("The diff(1) program is required for showing archive differences, please install it")
+        msg = "The diff(1) program is required for showing archive differences, please install it."
+        raise util.PatoolError(msg)
     tmpdir1 = util.tmpdir()
     tmpdir2 = util.tmpdir()
     try:
@@ -486,6 +494,9 @@ def _diff_archives (archive1, archive2, **kwargs):
 
 def _repack_archive (archive1, archive2, **kwargs):
     """Repackage an archive to a different format."""
+    if util.is_same_file(archive1, archive2):
+        msg = "cannot repack identical archives `%s' and `%s'"
+        raise util.PatoolError(msg % (archive1, archive2))
     tmpdir = util.tmpdir()
     try:
         _handle_archive(archive1, 'extract', outdir=tmpdir, **kwargs)
@@ -539,7 +550,6 @@ def test (archive, verbose=False):
 
 def create (archive, *filenames, **kwargs):
     """Create given archive with given files."""
-    assert len(filenames) > 0
     return handle_archive(archive, 'create', *filenames, **kwargs)
 
 
diff --git a/patoolib/util.py b/patoolib/util.py
index 95bb3c8..6776747 100644
--- a/patoolib/util.py
+++ b/patoolib/util.py
@@ -189,7 +189,7 @@ def guess_mime_file_mime (file_prog, filename):
         cmd = [file_prog, "--brief", "--mime", "--uncompress", filename]
         try:
             outparts = backtick(cmd).strip().split(";")
-        except OSError, msg:
+        except OSError:
             # ignore errors, as file(1) is only a fallback
             return mime, encoding
         mime2 = outparts[0].split(" ", 1)[0]
@@ -250,7 +250,7 @@ def guess_mime_file_text (file_prog, filename):
     cmd = [file_prog, "--brief", filename]
     try:
         output = backtick(cmd).strip()
-    except OSError, msg:
+    except OSError:
         # ignore errors, as file(1) is only a fallback
         return None
     # match output against known strings
@@ -260,14 +260,28 @@ def guess_mime_file_text (file_prog, filename):
     return None
 
 
-def check_filename (filename):
+def check_existing_filename (filename):
     """Ensure that given filename is a valid, existing file."""
     if not os.path.isfile(filename):
-        raise PatoolError("`%s' is not a file." % filename)
+        raise PatoolError("`%s' is not a file" % filename)
     if not os.path.exists(filename):
-        raise PatoolError("File `%s' not found." % filename)
+        raise PatoolError("file `%s' was not found" % filename)
     if not os.access(filename, os.R_OK):
-        raise PatoolError("File `%s' not readable." % filename)
+        raise PatoolError("file `%s' is not readable" % filename)
+
+
+def check_new_filename (filename):
+    """Check that filename does not already exist."""
+    if os.path.exists(filename):
+        raise PatoolError("cannot overwrite existing file `%s'" % filename)
+
+
+def check_archive_filelist (filenames):
+    """Check that file list is not empty and contains only existing files."""
+    if not filenames:
+        raise PatoolError("cannot create archive with empty filelist")
+    for filename in filenames:
+        check_existing_filename(filename)
 
 
 def set_mode (filename, flags):
@@ -387,3 +401,10 @@ def strlist_with_or (alist):
     if len(alist) > 1:
         return "%s or %s" % (", ".join(alist[:-1]), alist[-1])
     return ", ".join(alist)
+
+
+def is_same_file (filename1, filename2):
+    """Check if filename1 and filename2 point to the same file object."""
+    if os.name == 'posix':
+        return os.path.samefile(filename1, filename2)
+    return os.path.realpath(filename1) == os.path.realpath(filename2)