def is_palindrome(n):
    """
    Fill in the blanks '_____' to check if a number
    is a palindrome.

    >>> is_palindrome(12321)
    True
    >>> is_palindrome(42)
    False
    >>> is_palindrome(2015)
    False
    >>> is_palindrome(55)
    True
    """
    x, y = n, 0
    f = lambda: y * 10 + x % 10
    while x > 0:
        x, y = x // 10, f()
    return y == n