[Tutor] Sorting Dictionary Keys

[FT]

Jim,

OK, use the example below for sorting dictionary keys and placing them in a
list. Note that an error will happen if the format on the print statement
does not correspond to the type of sort.


#THIS SORTS A DICTIONARY BY USING SET THEORY AND DIC ITEMS!
import random
dic = {}
print "Randomizing!"
for i in range(20):
    dic[ random.randrange(100)] = random.randrange(100, 1000)
print "Dic:"
j=0
list=[]
for k,i in dic.items():
    print "K=%d I=%d" % (k,i)
    list.append("K=%d I=%d" % (k,i))
    j+=1

j=0
print "Sorted Dic By Set:"
print "Num: Old,  Sorted"
for k in sorted(set(dic)):
    print "(%d) %s | K=%d I=%d" % (j+1, list[j], k,dic[k])
    j+=1

j=0
print "Sorted Dic By Items:"
print "Num: Old,  Sorted"
for k,i in sorted(dic.items()):
    print "(%d) %s | K=%d I=%d" % (j+1, list[j], k,i)
    j+=1


--- On Tue, 5/13/08, James Hartley <jjhartley at gmail.com> wrote:

  From: James Hartley <jjhartley at gmail.com>
  Subject: [Tutor] sorting dictionary keys?
  To: tutor at python.org
  Date: Tuesday, May 13, 2008, 11:06 AM


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