4919.sagews

def symbolic_function(variables, *args, **kwds):
    def result(f):
        def evalf_func(self,x,parent=None):
            if parent == None:
                return f(x)
            else:
                return parent(f(x))
        return function(f.__name__, variables, evalf_func=evalf_func, *args, **kwds).operator()
        
    return result

@symbolic_function(x)
def steps(x):
    if x < 0:
        return -x
    elif x < 3:
        return x
    else:
        return 3

steps(5)

$\renewcommand{\Bold}[1]{\mathbf{#1}}{\rm steps}\left(5\right)$

n(steps(5))

$\renewcommand{\Bold}[1]{\mathbf{#1}}3.00000000000000$

plot(steps(x),(x,-3,6))