Merge sort error

Question

I was trying to create a merge sort function in python 3 IDLE and I can't find the problem with my code that provokes the interpreter to show the error. I need Help to understand what is the problem with my code.
Code:
def mergesort(a,b,c):
A=0
B=0
for i in range(len(a)+len(b)):
if (A==len(a)):
c+=b[B:]
break
elif (B==len(b)):
c+=a[A:]
break
elif (a[A]<=b[B]):
c[i]=a[A]
A=A+1
else:
c[i]=a[B]
B=B+1
print (c)
mergesort(list(range(10)),list(range(30,40)),[])
Error Message:
Traceback (most recent call last):
File "G:\STUDY FILES\EXTERNAL\COURSES\NPTEL COURSE\PYTHON STARTER\files\mergesort.py", line 18, in <module>
mergesort(list(range(10)),list(range(30,40)),[])
File "G:\STUDY FILES\EXTERNAL\COURSES\NPTEL COURSE\PYTHON STARTER\files\mergesort.py", line 12, in mergesort
c[i]=a[A]
IndexError: list assignment index out of range

Answer 1

I figured out the answer myself with both for loop and while loop💙..
thanq for helping me out💨 ..
def mergesort(a,b,c):
A=0
B=0
for i in range(len(a)+len(b)):
if (A==len(a)):
c=c+b[B:]
break
elif (B==len(b)):
c=c+a[A:]
break
elif (a[A]<=b[B]):
c=c+[a[A]]
A=A+1
else:
c=c+[b[B]]
B=B+1
print (c)
def merge(a,b,c):
A=0
B=0
while (A<len(a) and B<len(b)):
if (a[A]>=b[B]):
c=c+[b[B]]
B+=1
else:
c=c+[a[A]]
A+=1
if A==len(a):
c=c+b[B:]
else:
c=c+a[A:]
print (c)
mergesort(list(range(10)),list(range(5,20,2)),[])
merge(list(range(4)),list(range(5,20,2)),[])

Answer 2

# Python program for implementation of MergeSort
# Merges two subarrays of arr[].
# First subarray is arr[l..m]
# Second subarray is arr[m+1..r]
def merge(arr, l, m, r):
n1 = m - l + 1
n2 = r- m
# create temp arrays
L = [0] * (n1)
R = [0] * (n2)
# Copy data to temp arrays L[] and R[]
for i in range(0 , n1):
L[i] = arr[l + i]
for j in range(0 , n2):
R[j] = arr[m + 1 + j]
# Merge the temp arrays back into arr[l..r]
i = 0 # Initial index of first subarray
j = 0 # Initial index of second subarray
k = l # Initial index of merged subarray
while i < n1 and j < n2 :
if L[i] <= R[j]:
arr[k] = L[i]
i += 1
else:
arr[k] = R[j]
j += 1
k += 1
# Copy the remaining elements of L[], if there
# are any
while i < n1:
arr[k] = L[i]
i += 1
k += 1
# Copy the remaining elements of R[], if there
# are any
while j < n2:
arr[k] = R[j]
j += 1
k += 1
# l is for left index and r is right index of the
# sub-array of arr to be sorted
def mergeSort(arr,l,r):
if l < r:
# Same as (l+r)/2, but avoids overflow for
# large l and h
m = (l+(r-1))/2
# Sort first and second halves
mergeSort(arr, l, m)
mergeSort(arr, m+1, r)
merge(arr, l, m, r)
# Driver code to test above
arr = [12, 11, 13, 5, 6, 7]
n = len(arr)
print ("Given array is")
for i in range(n):
print ("%d" %arr[i]),
mergeSort(arr,0,n-1)
print ("\n\nSorted array is")
for i in range(n):
print ("%d" %arr[i]),