Fix issue jschneier#118

.gitignore

@@ -22,3 +22,4 @@ setuptools*
 __pycache__
 .coverage
 .cache
+.idea

AUTHORS

@@ -29,6 +29,7 @@ By order of apparition, thanks:
     * Matt Braymer-Hayes (S3 with Boto3)
     * Eirik Martiniussen Sylliaas (Google Cloud Storage native support)
     * Jody McIntyre (Google Cloud Storage native support)
+    * Stanislav Kaledin (Bug fixes in SFTPStorage)
 
 Extra thanks to Marty for adding this in Django,
 you can buy his very interesting book (Pro Django).

storages/backends/sftpstorage.py

@@ -53,11 +53,12 @@ def __init__(self, host=None, params=None, interactive=None, file_mode=None,
     def _connect(self):
         self._ssh = paramiko.SSHClient()
 
-        if self._known_host_file is not None:
+        known_host_file = self._known_host_file or os.path.expanduser(
+            os.path.join("~", ".ssh", "known_hosts")
+        )
+
+        if os.path.exists(known_host_file):
             self._ssh.load_host_keys(self._known_host_file)
-        else:
-            # automatically add host keys from current user.
-            self._ssh.load_host_keys(os.path.expanduser(os.path.join("~", ".ssh", "known_hosts")))
 
         # and automatically add new host keys for hosts we haven't seen before.
         self._ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
@@ -152,6 +153,7 @@ def delete(self, name):
     def exists(self, name):
         # Try to retrieve file info.  Return true on success, false on failure.
         remote_path = self._remote_path(name)
+
         try:
             self.sftp.stat(remote_path)
             return True

tests/test_sftp.py

@@ -17,6 +17,12 @@ def setUp(self):
     def test_init(self):
         pass
 
+    @patch('paramiko.SSHClient')
+    def test_no_known_hosts_file(self, mock_ssh):
+        self.storage._known_host_file = "not_existed_file"
+        self.storage._connect()
+        self.assertEqual('foo', mock_ssh.return_value.connect.call_args[0][0])
+
     @patch('paramiko.SSHClient')
     def test_connect(self, mock_ssh):
         self.storage._connect()