def base26(x, _alphabet=string.ascii_uppercase):
    """Return positive ``int`` ``x`` as string in bijective base26 notation.

    >>> [base26(i) for i in [0, 1, 2, 26, 27, 28, 702, 703, 704]]
    ['', 'A', 'B', 'Z', 'AA', 'AB', 'ZZ', 'AAA', 'AAB']

    >>> base26(344799)  # 19 * 26**3 + 16 * 26**2 + 1 * 26**1 + 13 * 26**0
    'SPAM'

    >>> base26(256)
    'IV'
    """
    result = []
    while x:
        x, digit = divmod(x, 26)
        if not digit:
            x -= 1
            digit = 26
        result.append(_alphabet[digit - 1])
    return ''.join(result[::-1])
Return positive ``int`` ``x`` as string in bijective base26 notation.

    >>> [base26(i) for i in [0, 1, 2, 26, 27, 28, 702, 703, 704]]
    ['', 'A', 'B', 'Z', 'AA', 'AB', 'ZZ', 'AAA', 'AAB']

    >>> base26(344799)  # 19 * 26**3 + 16 * 26**2 + 1 * 26**1 + 13 * 26**0
    'SPAM'

    >>> base26(256)
    'IV'