Minor fixes: bz2file dependency, paramiko warning handling (#309)

* move paramiko import and warning deeper into code

* improve register_compressor example

* fixup in deprecated smart_open function

multipart_upload_kwargs shouldn't contain endpoint_url.
That parameter is only for resource_kwargs.

* remove bz2file dependency, fix #300

* Revert "remove bz2file dependency, fix #300"

This reverts commit 84a008a.

* make bz2file a dependency only under Py2, fix #300

* re-raise ImportError on failure

setup.py

@@ -9,6 +9,8 @@
 
 import io
 import os
+import sys
+
 from setuptools import setup, find_packages
 
 
@@ -41,6 +43,14 @@ def _get_version():
     'google-compute-engine==2.8.12'
 ]
 
+install_requires = [
+    'boto >= 2.32',
+    'requests',
+    'boto3',
+]
+if sys.version_info[0] == 2:
+    install_requires.append('bz2file')
+
 setup(
     name='smart_open',
     version=_get_version(),
@@ -66,12 +76,7 @@ def _get_version():
     license='MIT',
     platforms='any',
 
-    install_requires=[
-        'boto >= 2.32',
-        'bz2file',
-        'requests',
-        'boto3',
-    ],
+    install_requires=install_requires,
     tests_require=tests_require,
     extras_require={
         'test': tests_require,

smart_open/smart_open_lib.py

@@ -81,11 +81,13 @@ def register_compressor(ext, callback):
     --------
 
     Instruct smart_open to use the identity function whenever opening a file
-    with a .foo extension:
+    with a .xz extension (see README.rst for the complete example showing I/O):
 
-    >>> def identity(file_obj, mode):
-    ...     return file_obj
-    >>> register_compressor('.foo', identity)
+    >>> def _handle_xz(file_obj, mode):
+    ...     import lzma
+    ...     return lzma.LZMAFile(filename=file_obj, mode=mode, format=lzma.FORMAT_XZ)
+    >>>
+    >>> register_compressor('.xz', _handle_xz)
 
     """
     if not (ext and ext[0] == '.'):

smart_open/ssh.py

@@ -28,11 +28,6 @@
 
 logger = logging.getLogger(__name__)
 
-try:
-    import paramiko
-except ImportError:
-    warnings.warn('paramiko missing, opening SSH/SCP/SFTP paths will be disabled.  `pip install paramiko` to suppress')
-
 #
 # Global storage for SSH connections.
 #
@@ -45,6 +40,15 @@
 
 
 def _connect(hostname, username, port):
+    try:
+        import paramiko
+    except ImportError:
+        warnings.warn(
+            'paramiko missing, opening SSH/SCP/SFTP paths will be disabled. '
+            '`pip install paramiko` to suppress'
+        )
+        raise
+
     key = (hostname, username)
     ssh = _SSH.get(key)
     if ssh is None: