safe type checking (isinstance instead of type-is)

Maintainer note: added changelog entry.
(cherry picked from commit 8917d83221f2422f1c4c3e6fb8538ea9e1f9a150)

2 files changed, 7 insertions, 4 deletions

diff --git a/CHANGES b/CHANGES
index 69c1caf7..be3b2ad7 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,9 @@ Temporary, post-Paramiko changelog while we get our sh!t together.
 
 * #15: Implemented parameter substitution in SSHConfig, matching the
   implementation of `ssh_config(5)`. Thanks to Olle Lundberg for the patch.
+* #24: Switch some internal type checking to use `isinstance` to help prevent
+  problems with client libraries using subclasses of builtin types. Thanks to
+  Alex Morega for the patch.
 
 ## ssh 1.7.13 (2012-02-13)
 
diff --git a/paramiko/sftp_client.py b/paramiko/sftp_client.py
index 79a77614..f446ba3d 100644
--- a/paramiko/sftp_client.py
+++ b/paramiko/sftp_client.py
@@ -641,13 +641,13 @@ class SFTPClient (BaseSFTP):
             msg = Message()
             msg.add_int(self.request_number)
             for item in arg:
-                if type(item) is int:
+                if isinstance(item, int):
                     msg.add_int(item)
-                elif type(item) is long:
+                elif isinstance(item, long):
                     msg.add_int64(item)
-                elif type(item) is str:
+                elif isinstance(item, str):
                     msg.add_string(item)
-                elif type(item) is SFTPAttributes:
+                elif isinstance(item, SFTPAttributes):
                     item._pack(msg)
                 else:
                     raise Exception('unknown type for %r type %r' % (item, type(item)))