argparse.FileType can be handy, but it doesn't create directories.

Be kind to the user and create the lock directory for them if it doesn't
exist.

src/bin/sage-flock

@@ -24,6 +24,32 @@ import pipes
 import sys
 
 
+class FileType(argparse.FileType):
+    """
+    Version of argparse.FileType with the option to ensure that the full path
+    to the file exists.
+    """
+
+    def __init__(self, mode='r', makedirs=False):
+        # Note, the base class __init__ takes other arguments too depending on
+        # the Python version but we don't care about them for this purpose
+        super(FileType, self).__init__(mode=mode)
+        self._makedirs = makedirs
+
+    def __call__(self, string):
+        if self._makedirs and string != '-':
+            dirname = os.path.dirname(string)
+            try:
+                os.makedirs(dirname)
+            except OSError as exc:
+                if not os.path.isdir(dirname):
+                    raise argparse.ArgumentTypeError(
+                            "can't create '{0}': {1}".format(dirname, exc))
+
+        return super(FileType, self).__call__(string)
+
+
+
 def main(argv=None):
     parser = argparse.ArgumentParser(description=__doc__)
     group = parser.add_mutually_exclusive_group()
@@ -34,7 +60,8 @@ def main(argv=None):
     # but supplying the --exclusive flag explicitly may help clarity
     group.add_argument('-x', '--exclusive', action='store_true',
                        help='create an exclusive lock (the default)')
-    parser.add_argument('lock', metavar='LOCK', type=argparse.FileType('w+'),
+    parser.add_argument('lock', metavar='LOCK',
+                        type=FileType('w+', makedirs=True),
                         help='filename of the lock')
     parser.add_argument('command', metavar='COMMAND', nargs=argparse.REMAINDER,
                         help='command to run with the lock including any '