Can anyone please help me in understanding the following python code

[bhk755 at gmail.com]

On Thursday, May 30, 2013 6:09:20 PM UTC+5:30, bhk... at gmail.com wrote:
> Thanks Chris, Wolfgang and Joshua for your replies.
> 
> 
> 
> ---
> 
> In step 2b, all the steps from 1 through 3 are executed again (twice). 
> 
> Soon, those calls will just output "Splitting" followed by "Merging"; 
> 
> and then we go back to 2c. That's why it *seems* that the code goes 
> 
> from 3 to 2c. You'll notice that the call depth decreases when this 
> 
> happens
> 
> 
> 
> Chris, Can you please let me know what makes the control of the program code go to  2c after the output "Merging". 
> 
> Also, please look into the following output for the same program with more print statements, 
> ---------------------------------------------- 
>  before calling main mergesort 
> 
>  Splitting [54, 26, 93, 17, 77, 31, 44, 55, 20]
> 
> left half before split  [54, 26, 93, 17]
> 
> right half before split [77, 31, 44, 55, 20]
> 
>   Splitting [54, 26, 93, 17]
> 
> left half before split  [54, 26]
> 
> right half before split [93, 17]
> 
>     Splitting [54, 26]
> 
> left half before split  [54]
> 
> right half before split [26]
> 
>       Splitting [54]
> 
>       Merging [54]
> 
>       Splitting [26]
> 
>       Merging [26]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [54]
> 
> right half after split [26]
> 
>     Merging [26, 54]
> 
>     Splitting [93, 17]
> 
> left half before split  [93]
> 
> right half before split [17]
> 
>       Splitting [93]
> 
>       Merging [93]
> 
>       Splitting [17]
> 
>       Merging [17]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [93]
> 
> right half after split [17]
> 
>     Merging [17, 93]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [26, 54]
> 
> right half after split [17, 93]
> 
>   Merging [17, 26, 54, 93]
> 
>   Splitting [77, 31, 44, 55, 20]
> 
> left half before split  [77, 31]
> 
> right half before split [44, 55, 20]
> 
>     Splitting [77, 31]
> 
> left half before split  [77]
> 
> right half before split [31]
> 
>       Splitting [77]
> 
>       Merging [77]
> 
>       Splitting [31]
> 
>       Merging [31]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [77]
> 
> right half after split [31]
> 
>     Merging [31, 77]
> 
>     Splitting [44, 55, 20]
> 
> left half before split  [44]
> 
> right half before split [55, 20]
> 
>       Splitting [44]
> 
>       Merging [44]
> 
>       Splitting [55, 20]
> 
> left half before split  [55]
> 
> right half before split [20]
> 
>         Splitting [55]
> 
>         Merging [55]
> 
>         Splitting [20]
> 
>         Merging [20]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [55]
> 
> right half after split [20]
> 
>       Merging [20, 55]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [44]
> 
> right half after split [20, 55]
> 
>     Merging [20, 44, 55]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [31, 77]
> 
> right half after split [20, 44, 55]
> 
>   Merging [20, 31, 44, 55, 77]
> 
> 
> 
> HERE AFTER SPLIT
> 
> 
> 
> left half after split [17, 26, 54, 93]
> 
> right half after split [20, 31, 44, 55, 77]
> 
>  Merging [17, 20, 26, 31, 44, 54, 55, 77, 93]
> 
> 
> 
>  after calling main mergesort
> 
> 
> 
> [17, 20, 26, 31, 44, 54, 55, 77, 93]
> 
> -------------------------------------------------------
>  
> In the above output, the control goes to "HERE AFTER SPLIT" after the "Merging" statement which is of-course the last statement in the function.On what condition this is happening.
> 
> Ideally as per my understanding, after the last statement of a function the control should come out of the function. 
> 
> Please correct me if I am wrong here.
> 
> There is something with respect-to functions in python that I am not able to understand.