In computer science, merge sort (also normally spelled mergesort) is an efficient, general-purpose, comparison-based sorting algorithm. A detailed description and analysis of bottom-up mergesort looked in a report by Goldstine and von Neumann as early as 1948.

Repeatedly merge sublists to produce new sorted sublists until there is only one sublist remaining. divide the unsorted list into N sublists, each containing one component (a list of one component is considered sorted).

```
"""
This is a pure Python implementation of the merge sort algorithm
For doctests run following command:
python -m doctest -v merge_sort.py
or
python3 -m doctest -v merge_sort.py
For manual testing run:
python merge_sort.py
"""
def merge_sort(collection):
"""Pure implementation of the merge sort algorithm in Python
:param collection: some mutable ordered collection with heterogeneous
comparable items inside
:return: the same collection ordered by ascending
Examples:
>>> merge_sort([0, 5, 3, 2, 2])
[0, 2, 2, 3, 5]
>>> merge_sort([])
[]
>>> merge_sort([-2, -5, -45])
[-45, -5, -2]
"""
def merge(left, right):
"""merge left and right
:param left: left collection
:param right: right collection
:return: merge result
"""
result = []
while left and right:
result.append((left if left[0] <= right[0] else right).pop(0))
return result + left + right
if len(collection) <= 1:
return collection
mid = len(collection) // 2
return merge(merge_sort(collection[:mid]), merge_sort(collection[mid:]))
if __name__ == "__main__":
user_input = input("Enter numbers separated by a comma:\n").strip()
unsorted = [int(item) for item in user_input.split(",")]
print(*merge_sort(unsorted), sep=",")
```