How to add the missing keys in this dictionary with values as empty string using python

Question

the dictionary sample is as below :

d = { 1:'',2:'',3:'',5:'',6:'2',7:'',9:'',10:'6',11:'7',13:'9',14:'',15:'11'}

and i want to add key 4 with empty string as value after key 3, key 8 with empty string as value after key 7 and so on ....I want the simplest code in python.

John La Rooy · Accepted Answer · 2013-02-18 13:56:07Z

5

>>> d = { 1:'',2:'',3:'',5:'',6:'2',7:'',9:'',10:'6',11:'7',13:'9',14:'',15:'11'}
>>> d.update(dict.fromkeys(set(range(16)).difference(d), ''))
>>> d
{0: '', 1: '', 2: '', 3: '', 4: '', 5: '', 6: '2', 7: '', 8: '', 9: '', 10: '6', 11: '7', 12: '', 13: '9', 14: '', 15: '11'}

Note that the dict is unordered, even though it may look ordered in this example!

answered Feb 18, 2013 at 13:56

John La Rooy

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1 Comment

Rituraj Ramteke Over a year ago

@Gnibber Thanks Gnibber, Your answer seems useful for me and I will be using it in my application code.

Martijn Pieters · Accepted Answer · 2014-07-07 07:09:26Z

2

Python dictionaries do not maintain an order. You cannot add anything 'after' another key.

Just add the keys you are missing:

d.update((missing, '') for missing in set(range(1, max(d) + 1)).difference(d))

which is a compact way of saying:

for index in range(1, max(d) + 1):  # all numbers from 1 to the highest value in the dict
    if index not in d:              # index is missing
        d[index] = ''               # add an empty entry

However, it looks more like you need a list instead:

alist = [None, '', '', '', '', '', '2', '', '', '', '6', '7', '', '9', '', '11']

where alist[15] returns '11' just like your d. The None at the start makes it easier to treat this whit 1-based indexing instead of 0-based, you could adjust your code for that otherwise.

edited Jul 7, 2014 at 7:09

answered Feb 18, 2013 at 13:43

Martijn Pieters

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5 Comments

mgilson Over a year ago

I suppose you could also use d.setdefault in your loop as well to avoid the index in d business...

Martijn Pieters Over a year ago

@mgilson: Since the loop is meant to illustrate what the code above it does, I think .setdefault() would only muddle the waters more.

Rituraj Ramteke Over a year ago

@MartijnPieters It seems that you are generating a list but I need to add my missing keys in the dictionary. The dictionary contains only numeric keys to they can be generated. I think you should take a reference of Above answer.

Martijn Pieters Over a year ago

@RiturajRamteke: That is what my answer does, generate the missing keys. But, a dictionary is an inefficient data structure if you wanted to map integers to values, where those integers are in a contiguous sequence. I am advising you to consider using a list instead.

Martijn Pieters Over a year ago

@RiturajRamteke: the dict.fromkeys() method is slightly more efficient, because indeed all that varies here is the keys, not the value, so in that respect gnibbler's solution is better, for updating your dictionary.

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