Using a mutable default function argument is bad

Python function arguments can have default values.  These values are
objects that are created when the "def" statement is run, not when the
function is called.  These objects are thus persistent across calls to
that function.  If a mutable object, such as a list, is used as a
default argument, that object will retain its value across function
calls.  This is potentially unwanted behavior if the function is called
multiple times.

Fix up function argument defaults in stgit/git.py, for safety.

Signed-off-by: Chuck Lever <cel@netapp.com>

diff --git a/stgit/git.py b/stgit/git.py
index 313779770da90665ceea4349f1ee60201212dee2..413604c0d05b977eb1a86a79c9d2c2d4658fc683 100644 (file)
--- a/stgit/git.py
+++ b/stgit/git.py
@@ -171,12 +171,14 @@ def __run(cmd, args=None):
 def __check_base_dir():
     return os.path.isdir(base_dir)
 
-def __tree_status(files = [], tree_id = 'HEAD', unknown = False,
+def __tree_status(files = None, tree_id = 'HEAD', unknown = False,
                   noexclude = True):
     """Returns a list of pairs - [status, filename]
     """
     refresh_index()
 
+    if not files:
+        files = []
     cache_files = []
 
     # unknown files
@@ -377,9 +379,12 @@ def rm(files, force = False):
         if files:
             __run('git-update-index --force-remove --', files)
 
-def update_cache(files = [], force = False):
+def update_cache(files = None, force = False):
     """Update the cache information for the given files
     """
+    if not files:
+        files = []
+
     cache_files = __tree_status(files)
 
     # everything is up-to-date
@@ -405,12 +410,17 @@ def update_cache(files = [], force = False):
 
     return True
 
-def commit(message, files = [], parents = [], allowempty = False,
+def commit(message, files = None, parents = None, allowempty = False,
            cache_update = True, tree_id = None,
            author_name = None, author_email = None, author_date = None,
            committer_name = None, committer_email = None):
     """Commit the current tree to repository
     """
+    if not files:
+        files = []
+    if not parents:
+        parents = []
+
     # Get the tree status
     if cache_update and parents != []:
         changes = update_cache(files)
@@ -473,10 +483,13 @@ def merge(base, head1, head2):
     if __run('git-merge-index -o -q gitmergeonefile.py -a') != 0:
         raise GitException, 'git-merge-index failed (possible conflicts)'
 
-def status(files = [], modified = False, new = False, deleted = False,
+def status(files = None, modified = False, new = False, deleted = False,
            conflict = False, unknown = False, noexclude = False):
     """Show the tree status
     """
+    if not files:
+        files = []
+
     cache_files = __tree_status(files, unknown = True, noexclude = noexclude)
     all = not (modified or new or deleted or conflict or unknown)
 
@@ -501,9 +514,11 @@ def status(files = [], modified = False, new = False, deleted = False,
         else:
             print '%s' % fs[1]
 
-def diff(files = [], rev1 = 'HEAD', rev2 = None, out_fd = None):
+def diff(files = None, rev1 = 'HEAD', rev2 = None, out_fd = None):
     """Show the diff between rev1 and rev2
     """
+    if not files:
+        files = []
 
     if rev2:
         diff_str = _output(['git-diff-tree', '-p', rev1, rev2] + files)
@@ -516,9 +531,11 @@ def diff(files = [], rev1 = 'HEAD', rev2 = None, out_fd = None):
     else:
         return diff_str
 
-def diffstat(files = [], rev1 = 'HEAD', rev2 = None):
+def diffstat(files = None, rev1 = 'HEAD', rev2 = None):
     """Return the diffstat between rev1 and rev2
     """
+    if not files:
+        files = []
 
     p=popen2.Popen3('git-apply --stat')
     diff(files, rev1, rev2, p.tochild)
@@ -548,9 +565,12 @@ def barefiles(rev1, rev2):
 
     return str.rstrip()
 
-def checkout(files = [], tree_id = None, force = False):
+def checkout(files = None, tree_id = None, force = False):
     """Check out the given or all files
     """
+    if not files:
+        files = None
+
     if tree_id and __run('git-read-tree -m', [tree_id]) != 0:
         raise GitException, 'Failed git-read-tree -m %s' % tree_id