python: Let RHashtable be returned as a Python dict.

The initial proposal was suggested by Matt Booth and discussed on the
mailing list here:

https://www.redhat.com/archives/libguestfs/2013-April/msg00007.html

python/examples/create_disk.py

@@ -5,7 +5,11 @@ import guestfs
 
 output = "disk.img"
 
-g = guestfs.GuestFS ()
+# All new Python code should pass python_return_dict=True
+# to the constructor.  It indicates that your program wants
+# to receive Python dicts for methods in the API that return
+# hashtables.
+g = guestfs.GuestFS (python_return_dict=True)
 
 # Create a raw-format sparse disk image, 512 MB in size.
 f = open (output, "w")

python/examples/guestfs-python.pod

@@ -7,7 +7,7 @@ guestfs-python - How to use libguestfs from Python
 =head1 SYNOPSIS
 
  import guestfs
- g = guestfs.GuestFS ()
+ g = guestfs.GuestFS (python_return_dict=True)
  g.add_drive_opts ("disk.img", format="raw", readonly=1)
  g.launch ()
 
@@ -18,6 +18,17 @@ programming language.  This page just documents the differences from
 the C API and gives some examples.  If you are not familiar with using
 libguestfs, you also need to read L<guestfs(3)>.
 
+=head2 python_return_dict=True
+
+All new code should construct the handle using:
+
+ g = guestfs.GuestFS (python_return_dict=True)
+
+This indicates that your program wants to receive Python dicts for
+methods in the API that return hashtables.
+
+In a future version of libguestfs, this will become the default.
+
 =head2 EXCEPTIONS
 
 Errors from libguestfs functions are mapped into C<RuntimeException>

python/examples/inspect_vm.py

@@ -6,7 +6,11 @@ import guestfs
 assert (len (sys.argv) == 2)
 disk = sys.argv[1]
 
-g = guestfs.GuestFS ()
+# All new Python code should pass python_return_dict=True
+# to the constructor.  It indicates that your program wants
+# to receive Python dicts for methods in the API that return
+# hashtables.
+g = guestfs.GuestFS (python_return_dict=True)
 
 # Attach the disk image read-only to libguestfs.
 g.add_drive_opts (disk, readonly=1)
@@ -35,17 +39,10 @@ for root in roots:
     # Sort keys by length, shortest first, so that we end up
     # mounting the filesystems in the correct order.
     mps = g.inspect_get_mountpoints (root)
-    def compare (a, b):
-        if len(a[0]) > len(b[0]):
-            return 1
-        elif len(a[0]) == len(b[0]):
-            return 0
-        else:
-            return -1
-    mps.sort (compare)
-    for mp_dev in mps:
+    def compare (a, b): return len(a) - len(b)
+    for device in sorted (mps.keys(), compare):
         try:
-            g.mount_ro (mp_dev[1], mp_dev[0])
+            g.mount_ro (mps[device], device)
         except RuntimeError as msg:
             print "%s (ignored)" % msg