Python/project_euler/problem_03/sol2.py

"""
Problem:
The prime factors of 13195 are 5,7,13 and 29. What is the largest prime factor
of a given number N?

e.g. for 10, largest prime factor = 5. For 17, largest prime factor = 17.
"""
from __future__ import print_function, division

try:
    raw_input  # Python 2
except NameError:
    raw_input = input  # Python 3


def solution(n):
    """Returns the largest prime factor of a given number n.

    >>> solution(13195)
    29
    >>> solution(10)
    5
    >>> solution(17)
    17
    >>> solution(3.4)
    3
    >>> solution(0)
    Traceback (most recent call last):
        ...
    ValueError: Parameter n must be greater or equal to one.
    >>> solution(-17)
    Traceback (most recent call last):
        ...
    ValueError: Parameter n must be greater or equal to one.
    >>> solution([])
    Traceback (most recent call last):
        ...
    TypeError: Parameter n must be int or passive of cast to int.
    >>> solution("asd")
    Traceback (most recent call last):
        ...
    TypeError: Parameter n must be int or passive of cast to int.
    """
    try:
        n = int(n)
    except (TypeError, ValueError) as e:
        raise TypeError("Parameter n must be int or passive of cast to int.")
    if n <= 0:
        raise ValueError("Parameter n must be greater or equal to one.")
    prime = 1
    i = 2
    while i * i <= n:
        while n % i == 0:
            prime = i
            n //= i
        i += 1
    if n > 1:
        prime = n
    return int(prime)


if __name__ == "__main__":
    print(solution(int(raw_input().strip())))