def d(n, precision=50)

def d(n, precision=50):
    """
    Given x is either an int or a float with 12 or fewer digits,
    return decimal.Decimal(str(x)).

    This function appears in a simpler form in the 2nd ed. of
    _Python In a Nutshell_, p.373

    #>>> from decimal import Decimal as D
    #>>> decimal.getcontext().prec = 50
    #>>> D('234')**D('.555555555555555')
    #Decimal('20.712428960882622698237158800584555118350558990840')
    >>> d(234)**d(.555555555555555)
    Decimal('20.712428960882622698237158800584555118350558990840')
    >>> d(234, 25)**d(.555555555555555)
    Decimal('20.712428960882622698237158800584555118350558990840')
    >>> d(234)**d(.555555555555555, 25)
    Decimal('20.71242896088262269823716')
    >>> d(234)**d(.5555555555555557)
    float beginning 0.555 has too many digits.
    Maximum to maintain accuracy is 15
    (<http://www.wolframalpha.com/input/?i=234**.555555555555555>
    gives 20.71242896088262269823715880058455511835055899083967...)
    """
    import decimal
    from decimal import getcontext
    getcontext().prec = precision
    import sys
    from decimal import Decimal as D

    if isinstance(n, float):
        with decimal.localcontext() as ctx:
            ctx.prec = 15
            if D(str(n)) != +D(str(n)):
                print('float beginning', str(n)[:5], 'has too many digits.')
                print('Maximum to maintain accuracy is 15 digits')
                sys.exit()

    elif isinstance(n, int):
        pass
    else:
        raise TypeError("WTF you didn't pass me an int or a float")
    return D(str(n))