Removes native xz support

Updates `register_compressor` example to show xz decompression.

README.rst

@@ -77,7 +77,6 @@ Other examples of URLs that ``smart_open`` accepts::
     file:///home/user/file.bz2
     [ssh|scp|sftp]://username@host//path/file
     [ssh|scp|sftp]://username@host/path/file
-    file:///home/user/file.xz
 
 .. _doctools_after_examples:
 
@@ -161,20 +160,29 @@ The tests are also run automatically with `Travis CI <https://travis-ci.org/RaRe
 Supported Compression Formats
 -----------------------------
 
-``smart_open`` allows reading and writing gzip, bzip2 and xz files.
+``smart_open`` allows reading and writing gzip and bzip2 files.
 They are transparently handled over HTTP, S3, and other protocols, too, based on the extension of the file being opened.
-You can easily add support for other file extensions and compression formats:
+You can easily add support for other file extensions and compression formats.
+For example, to open xz-compressed files:
 
 .. code-block:: python
 
-    def _handle_lzma(file_obj, mode):
-        import lzma
-        return lzma.LZMAFile(filename=file_obj, mode=mode, format=lzma.FORMAT_ALONE)
-
+    import lzma, os
     from smart_open import open, register_compressor
-    register_compressor('.lzma', _handle_lzma)
-    with open('file.lzma', ...) as fin:
-        pass
+
+    def _handle_xz(file_obj, mode):
+        return lzma.LZMAFile(filename=file_obj, mode=mode, format=lzma.FORMAT_XZ)
+
+    register_compressor('.xz', _handle_xz)
+
+    data_path = './smart_open/tests/test_data/crime-and-punishment.txt.xz'
+    with open(data_path) as f:
+        crime_and_punishment = f.read()
+
+``lzma`` is in the standard library in Python 3.3 and greater.
+For 2.7, use `backports.lzma`_.
+
+.. _backports.lzma: https://pypi.org/project/backports.lzma/
 
 Transport-specific Options
 --------------------------

help.txt

@@ -50,8 +50,7 @@ FUNCTIONS
 
         - ``.gz``
         - ``.bz2``
-        - ``.xz``
-
+
         The function depends on the file extension to determine the appropriate codec.
 
         Parameters

setup.py

@@ -57,7 +57,6 @@ def read(fname):
         'bz2file',
         'requests',
         'boto3',
-        'backports.lzma;python_version<"3.3"',
     ],
     tests_require=tests_require,
     extras_require={

smart_open/smart_open_lib.py

@@ -107,24 +107,11 @@ def _handle_gzip(file_obj, mode):
     return gzip.GzipFile(fileobj=file_obj, mode=mode)
 
 
-def _handle_xz(file_obj, mode):
-    #
-    # Delay import of compressor library until we actually need it
-    #
-    try:
-        import lzma
-    except ImportError:
-        # py<3.3
-        from backports import lzma
-    return lzma.LZMAFile(filename=file_obj, mode=mode, format=lzma.FORMAT_XZ)
-
-
 #
 # NB. avoid using lambda here to make stack traces more readable.
 #
 register_compressor('.bz2', _handle_bz2)
 register_compressor('.gz', _handle_gzip)
-register_compressor('.xz', _handle_xz)
 
 
 Uri = collections.namedtuple(
@@ -224,7 +211,6 @@ def open(
 
     - ``.gz``
     - ``.bz2``
-    - ``.xz``
 
     The function depends on the file extension to determine the appropriate codec.
 
@@ -596,7 +582,6 @@ def _parse_uri(uri_as_string):
       * file:///home/user/file.bz2
       * [ssh|scp|sftp]://username@host//path/file
       * [ssh|scp|sftp]://username@host/path/file
-      * file:///home/user/file.xz
 
     """
     if os.name == 'nt':

smart_open/tests/test_smart_open.py

@@ -256,7 +256,7 @@ def _test_compressed_http(self, suffix, query):
         smart_open_object = smart_open.smart_open(
             'http://127.0.0.1/data%s%s' % (suffix, '?some_param=some_val' if query else ''))
 
-        # decompress the xz and get the same md5 hash
+        # decompress the file and get the same md5 hash
         self.assertEqual(smart_open_object.read(), raw_data)
 
     @unittest.skipIf(six.PY2, 'gzip support for Py2 is not implemented yet')
@@ -268,10 +268,6 @@ def test_http_bz2(self):
         """Can open bzip2 via http?"""
         self._test_compressed_http(".bz2", False)
 
-    def test_http_xz(self):
-        """Can open xz via http?"""
-        self._test_compressed_http(".xz", False)
-
     @unittest.skipIf(six.PY2, 'gzip support for Py2 is not implemented yet')
     def test_http_gz_query(self):
         """Can open gzip via http with a query appended to URI?"""
@@ -281,10 +277,6 @@ def test_http_bz2_query(self):
         """Can open bzip2 via http with a query appended to URI?"""
         self._test_compressed_http(".bz2", True)
 
-    def test_http_xz_query(self):
-        """Can open xz via http with a query appended to URI?"""
-        self._test_compressed_http(".xz", True)
-
 
 def make_buffer(cls=six.BytesIO, initial_value=None, name=None):
     """
@@ -1014,20 +1006,6 @@ def test_write_read_bz2(self):
         """Can write and read bz2?"""
         self.write_read_assertion('.bz2')
 
-    def test_write_read_xz(self):
-        """Can write and read xz2?"""
-        self.write_read_assertion('.xz')
-
-    def test_read_real_xz(self):
-        """Can read a real xz file."""
-        base_path = os.path.join(CURR_DIR, 'test_data/crime-and-punishment.txt')
-        head_path = os.path.join(CURR_DIR, 'test_data/crime-and-punishment.txt.xz')
-        with smart_open.smart_open(head_path) as f:
-            smart_data = f.read()
-        with open(base_path, 'rb') as f:
-            orig_data = f.read()
-        self.assertEqual(smart_data, orig_data)
-
 
 class MultistreamsBZ2Test(unittest.TestCase):
     """