For mutable object as a default parameter in function and method-declarations the problem is, that the evaluation and creation takes place at exactly the same moment. The python-parser reads the function-head and evaluates it at the same moment. Most beginers assume that a new object is created at every call, but that's not correct. One object (in your example a list) is created at the moment of declaration and not on demand when you are calling the method. For imutable objects that's not a problem, because even if all calls share the same object, it's imutable and therefore it's properties remain the same. As a convention, must be used the None object for defaults to indicate the use of a default initialization, which now can take place in the function-body, which naturally is evaluated at call-time. Signed-off-by: Ramon Medeiros <ramonn(a)linux.vnet.ibm.com&gt; --- disks.py | 4 +++- model/packagesupdate.py | 4 +++- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/disks.py b/disks.py index 2883431..a1ba7c2 100644 --- a/disks.py +++ b/disks.py @@ -47,7 +47,9 @@ def _get_dev_node_path(maj_min): return "/dev/%s" % data["DEVNAME"] -def _get_lsblk_devs(keys, devs=[]): +def _get_lsblk_devs(keys, devs=None): + if devs is None: + devs = [] out, err, returncode = run_command( ["lsblk", "-Pbo"] + [','.join(keys)] + devs ) diff --git a/model/packagesupdate.py b/model/packagesupdate.py index 073667c..42011f7 100644 --- a/model/packagesupdate.py +++ b/model/packagesupdate.py @@ -56,11 +56,13 @@ class PackageUpdateModel(object): return self.host_swupdate.getUpdate(name) - def _resolve_dependencies(self, package=None, dep_list=[]): + def _resolve_dependencies(self, package=None, dep_list=None): """ Resolve the dependencies for a given package from the dictionary of eligible packages to be upgraded. """ + if dep_list is None: + dep_list = [] if package is None: return [] dep_list.append(package)