'Returns the base 10 logarithm of self.'

def log10(self, context=None):

    if (context is None):
        context = getcontext()
    ans = self._check_nans(context=context)
    if ans:
        return ans
    if (not self):
        return _NegativeInfinity
    if (self._isinfinity() == 1):
        return _Infinity
    if (self._sign == 1):
        return context._raise_error(InvalidOperation, 'log10    of    a    negative    value')
    if ((self._int[0] == '1') and (self._int[1:] == ('0' * (len(self._int) - 1)))):
        ans = Decimal(((self._exp + len(self._int)) - 1))
    else:
        op = _WorkRep(self)
        (c, e) = (op.int, op.exp)
        p = context.prec
        places = ((p - self._log10_exp_bound()) + 2)
        while True:
            coeff = _dlog10(c, e, places)
            if (coeff % (5 * (10 ** ((len(str(abs(coeff))) - p) - 1)))):
                break
            places += 3
        ans = _dec_from_triple(int((coeff < 0)), str(abs(coeff)), (- places))
    context = context._shallow_copy()
    rounding = context._set_rounding(ROUND_HALF_EVEN)
    ans = ans._fix(context)
    context.rounding = rounding
    return ans
