git p4: add comments to p4BranchesInGit

Signed-off-by: Pete Wyckoff <pw@padd.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-p4.py

@@ -548,6 +548,12 @@ def gitConfigList(key):
     return _gitConfig[key]
 
 def p4BranchesInGit(branchesAreInRemotes=True):
+    """Find all the branches whose names start with "p4/", looking
+       in remotes or heads as specified by the argument.  Return
+       a dictionary of { branch: revision } for each one found.
+       The branch names are the short names, without any
+       "p4/" prefix."""
+
     branches = {}
 
     cmdline = "git rev-parse --symbolic "
@@ -559,15 +565,18 @@ def p4BranchesInGit(branchesAreInRemotes = True):
     for line in read_pipe_lines(cmdline):
         line = line.strip()
 
-        ## only import to p4/
-        if not line.startswith('p4/') or line == "p4/HEAD":
+        # only import to p4/
+        if not line.startswith('p4/'):
+            continue
+        # special symbolic ref to p4/master
+        if line == "p4/HEAD":
             continue
-        branch = line
 
-        # strip off p4
-        branch = re.sub ("^p4/", "", line)
+        # strip off p4/ prefix
+        branch = line[len("p4/"):]
 
         branches[branch] = parseRevision(line)
+
     return branches
 
 def findUpstreamBranchPoint(head = "HEAD"):