I have four ordinary differential equation written in mathmatica :

Simplify[DSolve[{y1'[x] == -0.162y1[x], y2'[x]=-0.148 y2[x]+ 0.055y1[x],y3'[x]==-0.134 y3[x]+ 0.033y1[x]+ 0.039y2[x],y4'[x]==-0.125y4[x]+0.021 y1[x]+0.025y2[x]+ 0.043y3[x], y1[0] == 100,y2[0]==4.76,y3[0]==69.7,y4[0]==0}, {y1[x], y2[x],y3[x],y4[x]}, x]]

I am trying to write them in python I have try the following :

def n1(y,x):
    s1 = 0.162131
    dydx = -s1 * y
    return dydx

def n2(y,x):
    s2 = 0.148234
    s12= 0.0555877 
    dydx2 = -s2 * y + s12 * n1(y,x)
    return dydx2

def n3(y,x):
    s3 = 0.134337
    s13= 0.0333526 
    s23= 0.0389114 
    dydx3 = -s3 * y + s13 * n1(y,x) + s23 * n2(y,x) 
    return dydx3

def n4(y,x):
    s4= 0.125072
    s14= 0.0213086
    s24= 0.0254777
    s34= 0.0430805
    dydt4 = -s4 * y + s14 * n1(y,x) + s24 * n2(y,x)  + s34 * n3(y,x) 
    return dydt4

## initial conditions
y01 = 100.
y02 = 4.74
y03 = 69.4
y04 = 0.    
x = np.linspace(0,20)

sol = odeint(n4,[y01,y02,y03,y04],x)

I want to solve n4 which include n1,n2,n3 , But I am only getting a solution for single equation??? I do not know what is wrong/missing to get the wright solution
Any help I appreciate that!!!