Fix dangerous-default value warnings

when default value is list or dict the default arguments are
instantiated as objects at the time of definition. This is significant
(exposing visible semantics) when the object is mutable. There’s no way
of re-binding that default argument name in the function’s closure. When
function is executed multiple times with its default value the value
will change between executions, possibly leading to strange side effects.

For more information see:
http://satran.in/2012/01/12/python-dangerous-default-value-as-argument.html

src/pylorax/imgutils.py

@@ -35,11 +35,13 @@ from pylorax.executils import runcmd, runcmd_output
 
 ######## Functions for making container images (cpio, tar, squashfs) ##########
 
-def compress(command, rootdir, outfile, compression="xz", compressargs=["-9"]):
+def compress(command, rootdir, outfile, compression="xz", compressargs=None):
     '''Make a compressed archive of the given rootdir.
     command is a list of the archiver commands to run
     compression should be "xz", "gzip", "lzma", "bzip2", or None.
     compressargs will be used on the compression commandline.'''
+    if compressargs is None:
+        compressargs = ["-9"]
     if compression not in (None, "xz", "gzip", "lzma", "bzip2"):
         raise ValueError, "Unknown compression type %s" % compression
     if compression == "xz":
@@ -68,17 +70,18 @@ def compress(command, rootdir, outfile, compression="xz", compressargs=["-9"]):
         [p.kill() for p in (find, archive, comp) if p]
         return 1
 
-def mkcpio(rootdir, outfile, compression="xz", compressargs=["-9"]):
+def mkcpio(rootdir, outfile, compression="xz", compressargs=None):
     return compress(["cpio", "--null", "--quiet", "-H", "newc", "-o"],
                     rootdir, outfile, compression, compressargs)
 
-def mktar(rootdir, outfile, compression="xz", compressargs=["-9"]):
+def mktar(rootdir, outfile, compression="xz", compressargs=None):
-    compressargs = compressargs or ["-9"]
     return compress(["tar", "--no-recursion", "--selinux", "--acls", "--xattrs", "-cf-", "--null", "-T-"],
                     rootdir, outfile, compression, compressargs)
 
-def mksquashfs(rootdir, outfile, compression="default", compressargs=[]):
+def mksquashfs(rootdir, outfile, compression="default", compressargs=None):
     '''Make a squashfs image containing the given rootdir.'''
+    if compressargs is None:
+        compressargs = []
     if compression != "default":
         compressargs = ["-comp", compression] + compressargs
     return execWithRedirect("mksquashfs", [rootdir, outfile] + compressargs)
@@ -303,7 +306,9 @@ def round_to_blocks(size, blocksize):
     return size
 
 # TODO: move filesystem data outside this function
-def estimate_size(rootdir, graft={}, fstype=None, blocksize=4096, overhead=128):
+def estimate_size(rootdir, graft=None, fstype=None, blocksize=4096, overhead=128):
+    if graft is None:
+        graft = {}
     getsize = lambda f: os.lstat(f).st_size
     if fstype == "btrfs":
         overhead = 64*1024 # don't worry, it's all sparse
@@ -422,12 +427,16 @@ class PartitionMount(object):
 
 ######## Functions for making filesystem images ##########################
 
-def mkfsimage(fstype, rootdir, outfile, size=None, mkfsargs=[], mountargs="", graft={}):
+def mkfsimage(fstype, rootdir, outfile, size=None, mkfsargs=None, mountargs="", graft=None):
     '''Generic filesystem image creation function.
     fstype should be a filesystem type - "mkfs.${fstype}" must exist.
     graft should be a dict: {"some/path/in/image": "local/file/or/dir"};
       if the path ends with a '/' it's assumed to be a directory.
     Will raise CalledProcessError if something goes wrong.'''
+    if mkfsargs is None:
+        mkfsargs = []
+    if graft is None:
+        graft = {}
     preserve = (fstype not in ("msdos", "vfat"))
     if not size:
         size = estimate_size(rootdir, graft, fstype)
@@ -448,18 +457,18 @@ def mkfsimage(fstype, rootdir, outfile, size=None, mkfsargs=[], mountargs="", gr
     runcmd(["sync"])
 
 # convenience functions with useful defaults
-def mkdosimg(rootdir, outfile, size=None, label="", mountargs="shortname=winnt,umask=0077", graft={}):
+def mkdosimg(rootdir, outfile, size=None, label="", mountargs="shortname=winnt,umask=0077", graft=None):
     mkfsimage("msdos", rootdir, outfile, size, mountargs=mountargs,
               mkfsargs=["-n", label], graft=graft)
 
-def mkext4img(rootdir, outfile, size=None, label="", mountargs="", graft={}):
+def mkext4img(rootdir, outfile, size=None, label="", mountargs="", graft=None):
     mkfsimage("ext4", rootdir, outfile, size, mountargs=mountargs,
               mkfsargs=["-L", label, "-b", "1024", "-m", "0"], graft=graft)
 
-def mkbtrfsimg(rootdir, outfile, size=None, label="", mountargs="", graft={}):
+def mkbtrfsimg(rootdir, outfile, size=None, label="", mountargs="", graft=None):
     mkfsimage("btrfs", rootdir, outfile, size, mountargs=mountargs,
                mkfsargs=["-L", label], graft=graft)
 
-def mkhfsimg(rootdir, outfile, size=None, label="", mountargs="", graft={}):
+def mkhfsimg(rootdir, outfile, size=None, label="", mountargs="", graft=None):
     mkfsimage("hfsplus", rootdir, outfile, size, mountargs=mountargs,
               mkfsargs=["-v", label], graft=graft)

src/pylorax/ltmpl.py

@@ -40,7 +40,9 @@ import sys, traceback
 import struct
 
 class LoraxTemplate(object):
-    def __init__(self, directories=["/usr/share/lorax"]):
+    def __init__(self, directories=None):
+        if directories is None:
+            directories = ["/usr/share/lorax"]
         # we have to add ["/"] to the template lookup directories or the
         # file includes won't work properly for absolute paths
         self.directories = ["/"] + directories
@@ -148,7 +150,9 @@ class LoraxTemplateRunner(object):
     * Commands should raise exceptions for errors - don't use sys.exit()
     '''
     def __init__(self, inroot, outroot, yum_obj=None, fatalerrors=True,
-                                        templatedir=None, defaults={}):
+                                        templatedir=None, defaults=None):
+        if defaults is None:
+            defaults = {}
         self.inroot = inroot
         self.outroot = outroot
         self.yum = yum_obj

src/pylorax/treebuilder.py

@@ -156,7 +156,9 @@ class RuntimeBuilder(object):
             runcmd(["depmod", "-a", "-F", ksyms, "-b", root, kver])
             generate_module_info(moddir+kver, outfile=moddir+"module-info")
 
-    def create_runtime(self, outfile="/var/tmp/squashfs.img", compression="xz", compressargs=[], size=2):
+    def create_runtime(self, outfile="/var/tmp/squashfs.img", compression="xz", compressargs=None, size=2):
+        if compressargs is None:
+            compressargs = []
         # make live rootfs image - must be named "LiveOS/rootfs.img" for dracut
         workdir = joinpaths(os.path.dirname(outfile), "runtime-workdir")
         os.makedirs(joinpaths(workdir, "LiveOS"))
@@ -192,13 +194,15 @@ class TreeBuilder(object):
     def kernels(self):
         return findkernels(root=self.vars.inroot)
 
-    def rebuild_initrds(self, add_args=[], backup="", prefix=""):
+    def rebuild_initrds(self, add_args=None, backup="", prefix=""):
         '''Rebuild all the initrds in the tree. If backup is specified, each
         initrd will be renamed with backup as a suffix before rebuilding.
         If backup is empty, the existing initrd files will be overwritten.
         If suffix is specified, the existing initrd is untouched and a new
         image is built with the filename "${prefix}-${kernel.version}.img"
         '''
+        if add_args is None:
+            add_args = []
         dracut = ["dracut", "--nomdadmconf", "--nolvmconf"] + add_args
         if not backup:
             dracut.append("--force")

src/sbin/lorax

@@ -244,8 +244,8 @@ def main(args):
               user_dracut_args=opts.dracut_args)
 
 
-def get_yum_base_object(installroot, repositories, mirrorlists=[], repo_files=[],
+def get_yum_base_object(installroot, repositories, mirrorlists=None, repo_files=None,
-                        tempdir="/var/tmp", proxy=None, excludepkgs=[],
+                        tempdir="/var/tmp", proxy=None, excludepkgs=None,
                         sslverify=True, releasever=None):
 
     def sanitize_repo(repo):
@@ -257,6 +257,13 @@ def get_yum_base_object(installroot, repositories, mirrorlists=[], repo_files=[]
         else:
             return None
 
+    if mirrorlists is None:
+        mirrorlists = []
+    if repo_files is None:
+        repo_files = []
+    if excludepkgs is None:
+        excludepkgs = []
+
     # sanitize the repositories
     repositories = map(sanitize_repo, repositories)
     mirrorlists = map(sanitize_repo, mirrorlists)