[Qemu-devel] [PATCH 02/11] qemu.py: Avoid dangerous arguments

[Lukáš Doktor]

The list object is mutable in python and potentially might modify other
object's arguments when used as default argument. Reproducer:

    >>> vm1 = QEMUMachine("qemu")
    >>> vm2 = QEMUMachine("qemu")
    >>> vm1._wrapper.append("foo")
    >>> print vm2._wrapper
    ['foo']

In this case the `args` is actually copied so it would be safe to keep
it, but it's not a good practice to keep it.

Signed-off-by: Lukáš Doktor <address@hidden>
---
 scripts/qemu.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/scripts/qemu.py b/scripts/qemu.py
index 191c916..66fd863 100644
--- a/scripts/qemu.py
+++ b/scripts/qemu.py
@@ -23,7 +23,7 @@ import qmp.qmp
 class QEMUMachine(object):
     '''A QEMU VM'''
 
-    def __init__(self, binary, args=[], wrapper=[], name=None,
+    def __init__(self, binary, args=None, wrapper=None, name=None,
                  test_dir="/var/tmp", monitor_address=None,
                  socket_scm_helper=None, debug=False):
         '''
@@ -39,6 +39,10 @@ class QEMUMachine(object):
         @param debug: enable debug mode (forwarded to QMP helper and such)
         @note: Qemu process is not started until launch() is used.
         '''
+        if args is None:
+            args = []
+        if wrapper is None:
+            wrapper = []
         if name is None:
             name = "qemu-%d" % os.getpid()
         if monitor_address is None:
-- 
2.9.4