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

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'}