python: is it possible to sort a dictionary by key?

Question

A previous stack overflow question on sorting a dictionary by key suggested the following for python 3.6+:

d={2:3,1:89,4:5,3:0}
b=dict(sorted(d.items()))
print(b)

And as expected the output is as follows:

{1: 89, 2: 3, 3: 0, 4: 5}

However when I enter the following

a={'1':1,'x':4,'z':-40023,'c':234}
c=dict(sorted(d.items()))
print(c) 

This is the output produced: {'1': 1, 'c': 234, 'x': 4, 'z': -40023 }

My questions are as follows:

1. Why does this approach work for the first case and not the second.
2. Why does it only work for python3.6+ and not before. Did they change the implementation of the dictionary class?
3. Is b in the above code a new sorted dictionary and if so how is that possible as I learned that hashtables are never ordered?

Answer 1

1. The second example is sorted correctly. See the ASCII table to verify that digits come before letters.

2. Python 3.6 (specifically the CPython implementation) changed the way dictionaries are implemented. A side effect of this change is that dictionaries retain the element insertion order, which can be very handy. This was just a side effect in 3.6, but the BDFL decreed that this change be made a feature of the language beginning with version 3.7.

3. b in your code above is indeed a new dict , and based on item 2 above, insertion order is retained. In this case, items are inserted in sorted order.