[Tutor] sorting dictionary keys?

[James Hartley]

I suspect this is a brain-dead question...

Given the following code, output is as expected:

$ cat test.py
d = { 'a' : 1, 'd' : 2, 'b' : 3, 'c' : 0 }

for i in d.keys():
    print "%s\t%s" % (i, d[i])
$ python test.py
a       1
c       0
b       3
d       2
$

But if the keys are sorted, I get an error:
$ cat test1.py
d = { 'a' : 1, 'd' : 2, 'b' : 3, 'c' : 0 }

for i in d.keys().sort():
    print "%s\t%s" % (i, d[i])
$ python test1.py
Traceback (most recent call last):
  File "test.py", line 3, in <module>
    for i in d.keys().sort():
TypeError: 'NoneType' object is not iterable
$

What is the correct manner to iterate through sorted dictionary keys?

Thanks.

Jim