Question: I am designing a software in Python and I was getting little curious about whether there is any time differences when popping out items from a dictionary of very small lengths and when popping out items from a dictionary of very large length or it is same in all cases.

Answer: 
You can easily answer this question for yourself using the `timeit` module. But the entire point of a dictionary is near-instant access to any desired element by key, so I would not *expect* to have a large difference between the two scenarios.
Check out this article on Python [TimeComplexity](http://wiki.python.org/moin/TimeComplexity):

> 
> The Average Case times listed for dict objects assume that the hash
>  function for the objects is sufficiently robust to make collisions
>  uncommon. The Average Case assumes the keys used in parameters are
>  selected uniformly at random from the set of all keys.
> 
> 
> Note that there is a fast-path for dicts that (in practice) only deal
>  with str keys; this doesn't affect the algorithmic complexity, but it
>  can significantly affect the constant factors: how quickly a typical
>  program finishes.
> 
> 
> 

According to this article, for a 'Get Item' operation, the average case is O(1), with a worse case of O(n). In other words, the worst case is that the time increases linearly with size. See [Big O Notation](http://en.wikipedia.org/wiki/Big_O_notation) on Wikipedia for more information.