Write a function largest in Python to which a list of integers can be passed as a parameter. The function should return the value of the largest number in the list as a result. If the given list does not contain any numbers, then the function should return the value None.

Example

>>> largest([2])
2
>>> largest([0, -2])
0
>>> largest([7, 1, 0, 7, 7, 1, 5])
7
>>> largest([9, 3, -1, 8])
9
>>> largest([-4, -8])
-4