sorting - recursive merge sort in python -

i trying make merge sort using 2 functions in python. got error like
indexerror: list assignment index out of range whenever run code. don't know part wrong.
code below. appreciate!!

def merge(a):      def merge_sort(a,first,last):         if first<last:             mid=(first+last)//2             merge_sort(a,first, mid)             merge_sort(a,mid+1,last)              temp=[]             temp.append(99999)             i=first             j=mid+1             k=0             while i<=mid , j<=last:                 if a[i]<=a[j]:                     temp[k]=a[i]                     k=k+1                     i=i+1                 else:                     temp[k]=a[j]                     k=k+1                     j=j+1             while i<=mid:                 temp[k]=a[i]                 k=k+1                 i=i+1             while j<=last:                 temp[k]=a[j]                 k=k+1                 j=j+1             a=0             b=first             while a<k:                 a[b]=temp[a]                 b=b+1                 a=a+1      merge_sort(a,0,len(a)-1)      return 

you can not assign value temp[k] long element not exist.

delete row temp.append(99999), replace every temp[k]=a[i] temp.append(a[i]) , every temp[k]=a[j] temp.append(a[j]).

you end with:

def merge(a):      def merge_sort(a,first,last):         if first<last:             mid=(first+last)//2             merge_sort(a,first, mid)             merge_sort(a,mid+1,last)              temp=[]             i=first             j=mid+1             k=0             while i<=mid , j<=last:                 if a[i]<=a[j]:                     temp.append(a[i])                     k=k+1                     i=i+1                 else:                     temp.append(a[j])                     k=k+1                     j=j+1             while i<=mid:                 temp.append(a[i])                 k=k+1                 i=i+1             while j<=last:                 temp.append(a[j])                 k=k+1                 j=j+1             a=0             b=first             while a<k:                 a[b]=temp[a]                 b=b+1                 a=a+1      merge_sort(a,0,len(a)-1)      return   = [1,9,4,5] print(a) print(merge(a)) 

output:

[1, 9, 4, 5] [1, 4, 5, 9]