diff -r 3f1deecd8d50 Lib/lzma.py
--- a/Lib/lzma.py	Sun Oct 13 00:36:08 2013 -0400
+++ b/Lib/lzma.py	Sun Oct 13 15:45:39 2013 +0800
@@ -54,9 +54,9 @@
         bytes object), in which case the named file is opened, or it can
         be an existing file object to read from or write to.
 
-        mode can be "r" for reading (default), "w" for (over)writing, or
-        "a" for appending. These can equivalently be given as "rb", "wb"
-        and "ab" respectively.
+        mode can be "r" for reading (default), "w" for (over)writing, "x" for
+        creating exclusively, or "a" for appending. These can equivalently be
+        given as "rb", "wb", "xb" and "ab" respectively.
 
         format specifies the container format to use for the file.
         If mode is "r", this defaults to FORMAT_AUTO. Otherwise, the
@@ -112,7 +112,7 @@
             self._decompressor = LZMADecompressor(**self._init_args)
             self._buffer = b""
             self._buffer_offset = 0
-        elif mode in ("w", "wb", "a", "ab"):
+        elif mode in ("w", "wb", "a", "ab", "x", "xb"):
             if format is None:
                 format = FORMAT_XZ
             mode_code = _MODE_WRITE
@@ -426,8 +426,8 @@
     object), in which case the named file is opened, or it can be an
     existing file object to read from or write to.
 
-    The mode argument can be "r", "rb" (default), "w", "wb", "a" or "ab"
-    for binary mode, or "rt", "wt" or "at" for text mode.
+    The mode argument can be "r", "rb" (default), "w", "wb", "x", "xb", "a",
+    or "ab" for binary mode, or "rt", "wt", "xt", or "at" for text mode.
 
     The format, check, preset and filters arguments specify the
     compression settings, as for LZMACompressor, LZMADecompressor and
diff -r 3f1deecd8d50 Lib/test/test_lzma.py
--- a/Lib/test/test_lzma.py	Sun Oct 13 00:36:08 2013 -0400
+++ b/Lib/test/test_lzma.py	Sun Oct 13 15:45:39 2013 +0800
@@ -362,6 +362,8 @@
             pass
         with LZMAFile(BytesIO(), "w") as f:
             pass
+        with LZMAFile(BytesIO(), "x") as f:
+            pass
         with LZMAFile(BytesIO(), "a") as f:
             pass
 
@@ -389,13 +391,28 @@
             with LZMAFile(TESTFN, "ab"):
                 pass
 
+    def test_init_with_x_mode(self):
+        for mode in ("x", "xb"):
+            unlink(TESTFN)
+            with LZMAFile(TESTFN, mode):
+                pass
+            with self.assertRaises(FileExistsError):
+                with LZMAFile(TESTFN, mode):
+                    pass
+
     def test_init_bad_mode(self):
         with self.assertRaises(ValueError):
             LZMAFile(BytesIO(COMPRESSED_XZ), (3, "x"))
         with self.assertRaises(ValueError):
             LZMAFile(BytesIO(COMPRESSED_XZ), "")
         with self.assertRaises(ValueError):
-            LZMAFile(BytesIO(COMPRESSED_XZ), "x")
+            LZMAFile(BytesIO(COMPRESSED_XZ), "xt")
+        with self.assertRaises(ValueError):
+            LZMAFile(BytesIO(COMPRESSED_XZ), "x+")
+        with self.assertRaises(ValueError):
+            LZMAFile(BytesIO(COMPRESSED_XZ), "rx")
+        with self.assertRaises(ValueError):
+            LZMAFile(BytesIO(COMPRESSED_XZ), "wx")
         with self.assertRaises(ValueError):
             LZMAFile(BytesIO(COMPRESSED_XZ), "rt")
         with self.assertRaises(ValueError):
@@ -1022,8 +1039,6 @@
         with self.assertRaises(ValueError):
             lzma.open(TESTFN, "")
         with self.assertRaises(ValueError):
-            lzma.open(TESTFN, "x")
-        with self.assertRaises(ValueError):
             lzma.open(TESTFN, "rbt")
         with self.assertRaises(ValueError):
             lzma.open(TESTFN, "rb", encoding="utf-8")
@@ -1072,6 +1087,15 @@
             with lzma.open(bio, "rt", newline="\r") as f:
                 self.assertEqual(f.readlines(), [text])
 
+    def test_x_mode(self):
+        for mode in ("x", "xb", "xt"):
+            unlink(TESTFN)
+            with lzma.open(TESTFN, mode):
+                pass
+            with self.assertRaises(FileExistsError):
+                with lzma.open(TESTFN, mode):
+                    pass
+
 
 class MiscellaneousTestCase(unittest.TestCase):
 
diff -r 3f1deecd8d50 Misc/NEWS
--- a/Misc/NEWS	Sun Oct 13 00:36:08 2013 -0400
+++ b/Misc/NEWS	Sun Oct 13 15:45:39 2013 +0800
@@ -42,6 +42,9 @@
 Library
 -------
 
+- Issue #19201: Add "x" mode (exclusive creation) in opening file to lzma
+  module.
+
 - Issue #19218: Rename collections.abc to _collections_abc in order to
   speed up interpreter start.