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I am a beginner in Python . dont know how can i set the order in Dictionary? . i searched and came to know it could be done through from collections import OrderedDict but don't know how to use it. i am trying below mention code to compare two Dictionary but i am not getting the output in order .

d = { k[0]: k[1:] for k in a }
d2= { k[0]: k[1:] for k in b }
p = {i:j for i,j in d2.items() if i not in d} 
q = {i:j for i,j in d.items() if i not in d2}

Any idea how to do this ?

Updated Question :

i have a nested list . How to get each list of nested list in next line ?

[['Eth116/1/12        sales            connected 1         full    10G     Fabric Exte'], ['Eth116/1/13   marketing        connected 190       full    100                ']]

Expected Output :

Eth116/1/12        sales            connected 1         full    10G     Fabric Exte
Eth116/1/13   marketing        connected 190       full    100
Jinni
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    `d = OrderedDict((k[0], k[1:]) for k in a)`. – hiro protagonist Sep 25 '18 at 07:41
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    dictionaries are unordered, if you want order you need a list – Ryan Schaefer Sep 25 '18 at 07:54
  • If you need to retain the order in which keys were *added to the dictionary,* then yes, you need OrderedDict. If you need to order the keys by some function, keep using a standard dict and use `sorted(d.keys(), key=lambda k: d[k])` to get the keys sorted based on their values (or whatever other criterion you need). – kungphu Sep 25 '18 at 08:29
  • as a beginner in Python, you should concentrate on Python 3. In Python 3.7, dictionaries are ordered, in the C-Python 3.6 (the most common version) they are also ordered. – 576i Sep 25 '18 at 08:41

2 Answers2

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Dictionaries are unordered and there is not much you can do to change that, short of writing your own subclass of dict (not recommended). Using OrderedDict will work, as shown in hiro protagonists's comment, as long as you keep in mind that the order in an OrderedDict is the order of insertion and is not related to the values of the keys. (The same is true of the ordering of Python 3 dicts.) If a and b have the same elements but in a different order then the resulting OrderedDicts will not be equal, unless you sort a and b beforehand.

If you want to compare two dicts where you can't easily determine the order of insertion, you need a data structure that supports unordered comparisons. I didn't have your data so I had to make some up. I started with this input

>>> a
[[1, 3, 5, 7, 9], [4, 9, 14, 19, 24, 29, 34, 39], [8, 17, 26, 35, 44, 53, 62, 71], [9, 19, 29, 39, 49, 59, 69, 79, 89]]
>>> b
[[1, 3, 5, 7, 9], [4, 9, 14, 19, 24, 29, 34, 39], [8, 17, 26, 35, 44, 53, 62, 71]]

As you can see, a has one extra element beginning 9.

Modify your dictionary construction code to make the values tuples not lists, because the dict values need to be hashable for the next step to work:

>>> d = { k[0]: tuple(k[1:]) for k in a }
>>> d2= { k[0]: tuple(k[1:]) for k in b }

Then you can convert the dictionaries to sets to do an unordered comparison:

>>> s = set(d.items())
>>> s2 = set(d2.items())
>>> s == s2
False

And you can use the set operators to discover what the difference is:

>>> s2 <= s
True
>>> s - s2
set([(9, (19, 29, 39, 49, 59, 69, 79, 89))])
BoarGules
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  • so i manage to convert into nested list so that it will be in order. How to get each list in next line ? i have updated the question.. – Jinni Sep 25 '18 at 09:08
  • @Jinni That is a rather different question (nothing to do with ordering `dict`s) but you can output the list you present like this: `for item in mylist: print item[0]` – BoarGules Sep 25 '18 at 09:18
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As of python 3.6 dictionaries are ordered in python, ignore the above answer for pythons above that number!

see here, on stackoverflow

tantalus
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