Any way to properly pretty-print ordered dictionaries?

Question

I like the pprint module in Python. I use it a lot for testing and debugging. I frequently use the width option to make sure the output fits nicely within my terminal window

Answer 1

As a temporary workaround you can try dumping in JSON format. You lose some type information, but it looks nice and keeps the order.

import json

pprint(data, indent=4)
# ^ugly

print(json.dumps(data, indent=4))
# ^nice

Answer 2

To print an ordered dict, e.g.

from collections import OrderedDict

d=OrderedDict([
    ('a', OrderedDict([
        ('a1',1),
        ('a2','sss')
    ])),
    ('b', OrderedDict([
        ('b1', OrderedDict([
            ('bb1',1),
            ('bb2',4.5)])),
        ('b2',4.5)
    ])),
])

I do

def dict_or_OrdDict_to_formatted_str(OD, mode='dict', s="", indent=' '*4, level=0):
    def is_number(s):
        try:
            float(s)
            return True
        except ValueError:
            return False
    def fstr(s):
        return s if is_number(s) else '"%s"'%s
    if mode != 'dict':
        kv_tpl = '("%s", %s)'
        ST = 'OrderedDict([\n'; END = '])'
    else:
        kv_tpl = '"%s": %s'
        ST = '{\n'; END = '}'
    for i,k in enumerate(OD.keys()):
        if type(OD[k]) in [dict, OrderedDict]:
            level += 1
            s += (level-1)*indent+kv_tpl%(k,ST+dict_or_OrdDict_to_formatted_str(OD[k], mode=mode, indent=indent, level=level)+(level-1)*indent+END)
            level -= 1
        else:
            s += level*indent+kv_tpl%(k,fstr(OD[k]))
        if i!=len(OD)-1:
            s += ","
        s += "\n"
    return s

print dict_or_OrdDict_to_formatted_str(d)

Which yields

"a": {
    "a1": 1,
    "a2": "sss"
},
"b": {
    "b1": {
        "bb1": 1,
        "bb2": 4.5
    },
    "b2": 4.5
}

or

print dict_or_OrdDict_to_formatted_str(d, mode='OD')

which yields

("a", OrderedDict([
    ("a1", 1),
    ("a2", "sss")
])),
("b", OrderedDict([
    ("b1", OrderedDict([
        ("bb1", 1),
        ("bb2", 4.5)
    ])),
    ("b2", 4.5)
]))

Answer 3

def pprint_od(od):
    print "{"
    for key in od:
        print "%s:%s,\n" % (key, od[key]) # Fixed syntax
    print "}"

There you go ^^

for item in li:
    pprint_od(item)

or

(pprint_od(item) for item in li)

Answer 4

For python < 3.8 (e.g. 3.6):

Monkey patch pprint's sorted in order to prevent it from sorting. This will have the benefit of everything working recursively as well, and is more suitable than the json option for whoever needs to use e.g. width parameter:

import pprint
pprint.sorted = lambda arg, *a, **kw: arg

>>> pprint.pprint({'z': 1, 'a': 2, 'c': {'z': 0, 'a': 1}}, width=20)
{'z': 1,
 'a': 2,
 'c': {'z': 0,
       'a': 1}}

---

Edit: cleaning up

To clean up after this dirty business just run: pprint.sorted = sorted

For a really clean solution can even use a contextmanager:

import pprint
import contextlib

@contextlib.contextmanager
def pprint_ordered():
    pprint.sorted = lambda arg, *args, **kwargs: arg
    yield
    pprint.sorted = sorted

# usage:

with pprint_ordered():
    pprint.pprint({'z': 1, 'a': 2, 'c': {'z': 0, 'a': 1}}, width=20)

# without it    
pprint.pprint({'z': 1, 'a': 2, 'c': {'z': 0, 'a': 1}}, width=20)

# prints: 
#    
# {'z': 1,
#  'a': 2,
#  'c': {'z': 0,
#        'a': 1}}
#
# {'a': 2,
#  'c': {'a': 1,
#        'z': 0},
#  'z': 1}

Answer 5

You could redefine pprint() and intercept calls for OrderedDict's. Here's a simple illustration. As written, the OrderedDict override code ignores any optional stream, indent, width, or depth keywords that may have been passed, but could be enhanced to implement them. Unfortunately this technique doesn't handle them inside another container, such as a list of OrderDict's

from collections import OrderedDict
from pprint import pprint as pp_pprint

def pprint(obj, *args, **kwrds):
    if not isinstance(obj, OrderedDict):
        # use stock function
        return pp_pprint(obj, *args, **kwrds)
    else:
        # very simple sample custom implementation...
        print "{"
        for key in obj:
            print "    %r:%r" % (key, obj[key])
        print "}"

l = [10, 2, 4]
d = dict((('john',1), ('paul',2), ('mary',3)))
od = OrderedDict((('john',1), ('paul',2), ('mary',3)))
pprint(l, width=4)
# [10,
#  2,
#  4]
pprint(d)
# {'john': 1, 'mary': 3, 'paul': 2}

pprint(od)
# {
#     'john':1
#     'paul':2
#     'mary':3
# }

Answer 6

Here’s a way that hacks the implementation of pprint. pprint sorts the keys before printing, so to preserve order, we just have to make the keys sort in the way we want.

Note that this impacts the items() function. So you might want to preserve and restore the overridden functions after doing the pprint.

from collections import OrderedDict
import pprint

class ItemKey(object):
  def __init__(self, name, position):
    self.name = name
    self.position = position
  def __cmp__(self, b):
    assert isinstance(b, ItemKey)
    return cmp(self.position, b.position)
  def __repr__(self):
    return repr(self.name)

OrderedDict.items = lambda self: [
    (ItemKey(name, i), value)
    for i, (name, value) in enumerate(self.iteritems())]
OrderedDict.__repr__ = dict.__repr__

a = OrderedDict()
a[4] = '4'
a[1] = '1'
a[2] = '2'
print pprint.pformat(a) # {4: '4', 1: '1', 2: '2'}