Readably print out a python dict() sorted by key


Question

I would like to print a python dictionary to a file using PrettyPrinter (for human readability) but have the dictionary be sorted by key in the output file to further improve readability. So:

mydict = {'a':1, 'b':2, 'c':3}
pprint(mydict)

currently prints to

{'b':2,
 'c':3,
 'a':1}

I would like to PrettyPrint the dictionary but have it printed out sorted by key eg.

{'a':1,
 'b':2,
 'c':3}

What is the best way to do this?

1
74
9/25/2009 9:22:11 PM

Accepted Answer

Actually pprint seems to sort the keys for you under python2.5

>>> from pprint import pprint
>>> mydict = {'a':1, 'b':2, 'c':3}
>>> pprint(mydict)
{'a': 1, 'b': 2, 'c': 3}
>>> mydict = {'a':1, 'b':2, 'c':3, 'd':4, 'e':5}
>>> pprint(mydict)
{'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5}
>>> d = dict(zip("kjihgfedcba",range(11)))
>>> pprint(d)
{'a': 10,
 'b': 9,
 'c': 8,
 'd': 7,
 'e': 6,
 'f': 5,
 'g': 4,
 'h': 3,
 'i': 2,
 'j': 1,
 'k': 0}

But not always under python 2.4

>>> from pprint import pprint
>>> mydict = {'a':1, 'b':2, 'c':3, 'd':4, 'e':5}
>>> pprint(mydict)
{'a': 1, 'c': 3, 'b': 2, 'e': 5, 'd': 4}
>>> d = dict(zip("kjihgfedcba",range(11)))
>>> pprint(d)
{'a': 10,
 'b': 9,
 'c': 8,
 'd': 7,
 'e': 6,
 'f': 5,
 'g': 4,
 'h': 3,
 'i': 2,
 'j': 1,
 'k': 0}
>>> 

Reading the source code of pprint.py (2.5) it does sort the dictionary using

items = object.items()
items.sort()

for multiline or this for single line

for k, v in sorted(object.items()):

before it attempts to print anything, so if your dictionary sorts properly like that then it should pprint properly. In 2.4 the second sorted() is missing (didn't exist then) so objects printed on a single line won't be sorted.

So the answer appears to be use python2.5, though this doesn't quite explain your output in the question.

Python3 Update

Pretty print by sorted keys (lambda x: x[0]):

for key, value in sorted(dict_example.items(), key=lambda x: x[0]): 
    print("{} : {}".format(key, value))

Pretty print by sorted values (lambda x: x[1]):

for key, value in sorted(dict_example.items(), key=lambda x: x[1]): 
    print("{} : {}".format(key, value))
85
3/16/2018 5:40:52 AM

Another alternative :

>>> mydict = {'a':1, 'b':2, 'c':3}
>>> import json

Then with python2 :

>>> print json.dumps(mydict, indent=4, sort_keys=True) # python 2
{
    "a": 1, 
    "b": 2, 
    "c": 3
}

or with python 3 :

>>> print(json.dumps(mydict, indent=4, sort_keys=True)) # python 3
{
    "a": 1, 
    "b": 2, 
    "c": 3
}

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