def _eval_(self, x):
        """
        INPUT:

        -  ``x`` - a real number or a symbolic expression

        EXAMPLES::

            sage: dirac_delta(1)
            0
            sage: dirac_delta(0)
            dirac_delta(0)
            sage: dirac_delta(x)
            dirac_delta(x)
            sage: dirac_delta(exp(-10000000000000000000))
            0

        Evaluation test::

            sage: dirac_delta(x).subs(x=1)
            0
        """
        try:
            approx_x = ComplexIntervalField()(x)
            if bool(approx_x.imag() == 0):      # x is real
                if bool(approx_x.real() == 0):  # x is zero
                    return None
                else:
                    return 0
        except Exception:                     # x is symbolic
            pass
        return None

    def _evalf_(self, x, **kwds):
        """
        TESTS:

        Check that :trac:`16587` is fixed::

            sage: M = sgn(3/2, hold=True); M
            sgn(3/2)
            sage: M.n()
            1
            sage: h(x) = sgn(x)
            sage: h(pi).numerical_approx()
            1.00000000000000
        """
        if hasattr(x,'sign'): # First check if x has a sign method
            return x.sign()
        if hasattr(x,'sgn'): # or a sgn method
            return x.sgn()
        approx_x = ComplexIntervalField()(x)
        if bool(approx_x.imag() == 0):      # x is real
            if bool(approx_x.real() == 0):  # x is zero
                return ZZ(0)
            # Now we have a non-zero real
            if bool((approx_x**(0.5)).imag() == 0): # Check: x > 0
                return ZZ(1)
            else:
                return ZZ(-1)
        raise ValueError("Numeric evaluation of symbolic expression")

def _is_numerically_zero_CIF(x):
    from sage.rings.all import ComplexIntervalField
    try:
        approx_x = ComplexIntervalField()(x)
        if bool(approx_x.imag() == 0) and bool(approx_x.real() == 0):
            return True
    except:
        return False

    def _evalf_(self, x, **kwds):
        """
        TESTS::

            sage: h(x) = unit_step(x)
            sage: h(pi).numerical_approx()
            1.00000000000000
        """
        approx_x = ComplexIntervalField()(x)
        if bool(approx_x.imag() == 0):      # x is real
            if bool(approx_x.real() == 0):  # x is zero
                return 1
            # Now we have a non-zero real
            if bool((approx_x**(0.5)).imag() == 0): # Check: x > 0
                return 1
            else:
                return 0
        raise ValueError("Numeric evaluation of symbolic expression")