You can use ast.literal_eval():
Safely evaluate an expression node or a string containing a Python expression. The string or node provided may only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and None.
This can be used for safely evaluating strings containing Python expressions from untrusted sources without the need to parse the values oneself.
In your example:
from ast import literal_eval
s="(1,2,3,4,5),(5,4,3,2,1)"
l = literal_eval(s)
print l
# ((1, 2, 3, 4, 5), (5, 4, 3, 2, 1))
print [(x[0], x[-1]) for x in l]
# [(1, 5), (5, 1)]