ValueError: not enough values to unpack (expected 2, got 0) python if elif else statement for matplotlib

I have created code that calculates the maximum Lyapunov exponents against two parameters a and b. This plots ok, however there is a chunk of the graph that is white where the graph is collapsing due to my x and y values equalling zero. Therefore, I need to set these equal to say 100 or similar to prevent this from happening and producing a fully coloured meshgrid plot.

I have already tried if statements but I either get a syntax error or another error a.any() a.all() when I substitute one of these into my if statement it returns another error. I have tried if elif and else statements and returning values. There is an error in them statements returning

ValueError: not enough values to unpack (expected 2, got 0)

The equations are in another cell defined as functions.

#diff values of a and b looping 
a=np.linspace(0,6,80)
b=np.linspace(0,5,80)

def lyapunov(a,b):
    #initial conditions
    a,b = np.meshgrid(a,b)
    d = 0.1
    xold = 0.5
    yold = 0.01
    ee = 0.000001
   #xnew and ynew values
   for k in range(1000):
       xnew=f(a,b,xold,yold)
       ynew=g(b,d,xold,yold)
       xold = xnew
       yold = ynew

if np.any(xnew<ee) and np.any(ynew<ee):
    ml = 100
    return ml

elif np.any(xnew>ee) and np.any(ynew<ee):
    ml = 50
    return ml

else:
    ml=0   
    for l in range(100):
        ydash=1
        ml = ml + np.log(abs(e(a,b,xold,yold,ydash)))

        ydash = yz(a,b,xold,yold,ydash) 
        xold=f(a,b,xold,yold)
        yold=g(b,d,xold,yold)

    ml = (ml/(2*100))
    return  ml

z = lyapunov(a,b)
ax.set_title('Lyapunov Exponent')
c = ax.pcolormesh(z)
fig.colorbar(c)
plt.show()

I expect a completed mesh grid with no white of colour showing the system collapsing therefore very small 0 and therefore halfing the run time. At present only half the plot is coloured. ERROR is returning 'ValueError: not enough values to unpack (expected 2, got 0)