Can I avoid a sorted dictionary output after I've used pprint.pprint, in Python?

Question

The code is:

from pprint import pprint
d = {"b" : "Maria", "c" : "Helen", "a" : "George"}
pprint(d, width = 1)

The output is:

{'a': 'George',
'b': 'Maria',
'c': 'Helen'}

But, the desired output is:

{'b': 'Maria',
'c': 'Helen',
'a': 'George'}

Could this be done with pprint or is there another way?

Asked By: Maria Pantsiou

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Source

Answer 1

You should use OrderedDict from the collections library of python to keep the ordering constant

from collections import OrderedDict
from pprint import pprint
d = OrderedDict({"b" : "Maria", "c" : "Helen", "a" : "George"})
pprint(d, width = 1)

UPDATE:

Since output is important, you can use the following code, its a hack but you create a function to implement this feature:

from collections import OrderedDict
d = OrderedDict({"b" : "Maria", "c" : "Helen", "a" : "George"})
print('{', end='')
total_len = len(d)
current_index = 1
for key, value in d.items():
    print('''+key+'': '' + value+ ''', end='')
    if current_index<total_len:
        print(',')
    else:
        print('}')
    current_index += 1

Answered By: Arghya Saha

Answer 2

If you read the source of pprint.py you’ll find that in PrettyPrinter._pprint_dict(), the method responsible for formatting dicts:

def _pprint_dict(self, object, stream, indent, allowance, context, level):
    write = stream.write
    write('{')
    if self._indent_per_level > 1:
        write((self._indent_per_level - 1) * ' ')
    length = len(object)
    if length:
        items = sorted(object.items(), key=_safe_tuple)
        self._format_dict_items(items, stream, indent, allowance + 1,
                                context, level)
    write('}')

_dispatch[dict.__repr__] = _pprint_dict

There’s this line items = sorted(object.items(), key=_safe_tuple), so dict items are always sorted first before being processed for formatting, and you will have to override it yourself by copying and pasting it and removing the offending line in your own script:

import pprint as pp
def _pprint_dict(self, object, stream, indent, allowance, context, level):
    write = stream.write
    write('{')
    if self._indent_per_level > 1:
        write((self._indent_per_level - 1) * ' ')
    length = len(object)
    if length:
        self._format_dict_items(object.items(), stream, indent, allowance + 1,
                                context, level)
    write('}')
pp.PrettyPrinter._dispatch[dict.__repr__] = _pprint_dict

so that:

pp.pprint({"b" : "Maria", "c" : "Helen", "a" : "George"}, width=1)

will output (in Python 3.6+):

{'b': 'Maria',
 'c': 'Helen',
 'a': 'George'}

Answered By: blhsing

Answer 3

Python 3.8 or newer:

You can use sort_dicts=False to prevent it from sorting them alphabetically:

pprint.pprint(data, sort_dicts=False)

Python 3.7 or older:

Since Python 3.7 (or 3.6 in the case of cPython), dict preserves insertion order. For any version prior, you will need to use an OrderedDict to keep keys in order.

Although, from the doc on pprint:

Dictionaries are sorted by key before the display is computed.

This means pprint will break your desired order regardless.

Alternative method:

You can also use json.dumps to pretty print your data.

Code:

import json
from collections import OrderedDict

# For Python 3.6 and prior, use an OrderedDict
d = OrderedDict(b="Maria", c="Helen", a="George")

print(json.dumps(d, indent=1))

Output:

{
 "b": "Maria",
 "c": "Helen",
 "a": "George"
}

Answered By: Olivier Melançon

Answer 4

A more generic solution is to use unittest.mock.patch to override the built-in sorted function with a function that does nothing but return the given first argument:

import pprint
from unittest.mock import patch

def unsorted_pprint(*args, **kwargs):
    with patch('builtins.sorted', new=lambda l, **_: l):
        orig_pprint(*args, **kwargs)

orig_pprint = pprint.pprint
pprint.pprint = unsorted_pprint

so that:

pprint.pprint({"b" : "Maria", "c" : "Helen", "a" : "George"})

outputs:

{'b': 'Maria', 'c': 'Helen', 'a': 'George'}

Answered By: blhsing

Answer 5

As of Python 3.8, pprint has a sort_dicts keyword argument you can set to prevent it from sorting dictionary keys alphabetically. If you set it to false, it will use the default ordering of dictionaries (e.g. insertion order).

Example:

>>> from pprint import pprint
>>> pprint(dict(z=0, a=1), sort_dicts=False)
{'z': 0, 'a': 1}

Answered By: Edward D'Souza

Can I avoid a sorted dictionary output after I've used pprint.pprint, in Python?

Question:

Answers:

Python 3.8 or newer:

Python 3.7 or older:

Alternative method: